and its 

Treatment 



E. E HOUGHTON & CO 




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COPYRIGHT DEPOSm 



STEEL 

AND ITS TREATMENT 



By the 

METALLURGICAL STAFF 

OF 

E. F. HOUGHTON & COMPANY 



SECOND EDITION 
ILLUSTRATED 



1914 
PHILADELPHIA 



Me 



Copyright, 1914 
E. F. HOUGHTON 85 CO. 



©CI.A380796 

OCT 12 1914 



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FOREWORD 

FOR over forty years E. F. Houghton & Co. have 
been engaged in the manufacture of products used 
in the heat treatment of steel. 

During that period they have conducted a laboratory 
of research that they might best comprehend the re- 
quirements of the steel industries and thus produce the 
best products. 

This research work has been carried on by the metal- 
lurgic force of the Company, and for many years con- 
sisted mostly in absorbing the individual experience of 
each work where for the most part nothing more than 
rule of thumb methods were applied. 

During the last fifteen years the rapid development 
in the heat treatment of steel, owing to the increased 
demand for high-service machine parts, a more careful 
and scientific study of the heat treatment of steel has 
been possible, and this little work is nothing more or 
less than the collection of such data as has been obtained 
from time to time by our metallurgic force plus the cor- 
rection of palpable errors, the reconciling of seeming 
inconsistencies and the deduction of a code of principles. 

The object of this little work is to aid the reader in a 
clearer understanding of the wonderful metal — steel — in 
the hope that it will help improve the quality of output 
and the economy of operation. 

With this accomplished, all we aimed at, namely suc- 
cess, will have been attained. 



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Composition of Steel 

Steel is not a simple substance like pure iron, gold or copper, 
but a complex artificial product. It is composed of groupings of 
many elements which enter into its make-up like granite rock is 
built up of the minerals quartz, mica and feldspar. These ele- 
ments, as they may be called, are only visible with the aid of 
the microscope. 

The term micro-structure has been given to what is thus 
brought to one's view. Upon etching a highly polished piece of 
steel this granitic structure is made apparent through the action 
of the etching medium — acid or other corrosive or abrasive ma- 
terial — which affects the elements variously, causing each to 
assume a color or structure peculiar to itself. 

In the photo-micrograph (Fig. 1) are seen the elements making 
up a piece of steel; thus the light areas are known as Ferrite, 
while the dark network is called Pearlite, assuming that the steel 
is an alloy of iron and carbon. 

Mineralogical names have been given to the constituents of 
iron and steel, and pure iron, or rather carbonless iron, con- 
sidered as a microscopical constituent, has been called "Ferrite." 
The Ferrite of commercial grades of iron and steel is not pure 
iron, but rather a solid solution of iron holding small amounts 
of silicon, phosphorus and other impurities. 

Pearlite is a formation in steel made up of definite proportions 
of iron (Ferrite) and iron carbide (Cementite). The percentage 
of Pearlite in steel is in proportion to the percentage of carbon 
content. 

Cementite is a chemical combination of iron and carbon ap- 
proximately 93.3 per cent, of iron and 6.67 per cent, of carbon. 

Like most substances, these combinations of elements are 
decomposed by the action of heat, new ones being formed. 
Water at 60 degrees Fahr. is a liquid. It is likewise a liquid at 
211 degrees Fahr., but at 212 degrees Fahr., it becomes vapor 



6 STEEL AND ITS TREATMENT 

or steam. So the elements Ferrite and Pearlite remain as such 
up to a temperature of 749° C. (1380° Fahr.) to 845° C. (1480° 
Fahr.), depending upon the quantity of each present, when they 
decompose, forming a new constituent known as "Martensite," 
as shown in Fig. 2. 

Now this ".Martensite" differs materially in its properties 
from either Ferrite or PearHte in that, if preserved by quenching 
the steel, it will be found hard and brittle, while Ferrite and 
Pearlite are soft and tough. Again Ferrite and Pearlite attract 
the magnet under all conditions, while the new constituent, 
"Martensite" in its hot condition does not; but in its cold con- 
dition it acts the same as Ferrite and Pearlite. 

On account of the close relation existing between the treat- 
ment and structure of steel, and the structure and physical proper- 
ties, it is essential that one realizes the importance of gaining a 
knowledge of what is called the critical points in steel, in order to 
lay the foundation for its heat treatment. 

The Thermal Critical Points of Steel 

If one should watch the slow heating of a piece of steel in a 
furnace, it would be noted that the temperature of the steel 
gradually increases with the increasing heat of the furnace until 
a temperature is reached when the steel may become slightly 
darker or cooler than the furnace. As the heating is con- 
tinued the piece will again assume the temperature of the 
furnace. 

In the raising heat the darkening of the piece of steel is due 
to the absorption of the heat to convert Ferrite and Pearlite into 
Martensite. 

Now if the furnace be permitted to cool slowly, during some 
point in the process the steel may become brighter or visibly 
hotter than the furnace, after which it assumes its normal rate 
of cooling and continues on down to atmospheric temperatures. 



STEEL AND ITS TREATMENT 7 

This rise in temperature in cooling indicates a giving off of 
heat which is caused by the conversion of the Martensite back 
to Ferrite and PearUte. 



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8 STEEL AND ITS TREATMENT 

A transformation of the constituents composing the steel 
accompanies these thermal changes — as for example on heating, 
the decomposition of Ferrite and Pearlite to form Martensite, as 
mentioned above, or vice versa, the decomposition of the Mar- 
tensite into its constituents Ferrite and Pearlite, as the case 
may be, during cooling. 

The temperatures or points occurring during the heating and 
cooling when these changes take place are called the critical 
points of steel. To distinguish between these two points, or 
ranges of points as is actually the case, those occurring on the 
heating are termed " Decalescence " and those on the cooling 
" Recalescence " points. 





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Time Time Time Time 

Pure Iron Low Qsrhon Medium Carbon Steel High Carbon. 

Fig. 4. The Influence of Carbon on the Critical Points 



When the various critical points occurring in steel are con- 
sidered collectively, the range of temperature that they cover is 
called the critical range. The critical range may include one, 
two or three points. The meaning of the expressions ''Critical 
Range on Heating" and "Critical Range on Cooling" is obvious. 

The carbon percentage influences the location of the thermal 
points as is shown in diagram Fig. 4. 

These ranges have a value which is of great importance in 
practical work. 



STEEL AND ITS TREATMENT 9 

The decalescent and corresponding recalescent points do not 
occur at exactly the same temperature, the decalescent points 
generally occurring some 25° C. (77° Fahr.) to 50° C. (122° Fahr.) 
higher than the recalescent. For instance, in Fig. 3 you will 
note the point Ac is shown at 740° C. (1364° Fahr.), while the 
corresponding Ar point is 690° C. (1274° Fahr.). 

It does not follow, however, that these two points are not the 
opposite phases of the same phenomenon. The fact that the 
critical point on cooling lags behind the point on heating and 
vice versa is evidently a case of hysteresis, so often observed in 
physical phenomena, implying a resistence of certain bodies to 
undergo a transformation, when theoretically the transformation 
is due. 

The slower the process of heating and cooling, the nearer will 
the two points approach each other, so that with infinitely slow 
cooling and heating they would undoubtedly occur at exactly 
the same temperature. 

Mechanical Treatment of Steel 

The principal purpose of working steel is to shape it into the 
desired form. Its structure and physical properties are dependent 
on the care in working and the heats used. The mechanical work- 
ing aside from machining is classed under two heads, namely: 
"Hot" and "Cold" Working. 

The finest grain size obtainable is undoubtedly that existing 
just as the steel has passed through the critical range on a rising 
heat. Hence, starting out with steel just below its solidification 
on undisturbed cooling the grain size increases until the cooling 
has passed through the critical range, and the grain size, at this 
stage, will be the resultant size at the cold temperature. Taking 
the same piece of steel, for instance, having a coarse structure, 
and on heating there will be no change in grain size until the 
critical range is reached ; there the coarse crystals break up and 



10 STEEL AND ITS TREATMENT 

at the upper critical point form the finest possible structure. 
Continued heating, however, above this point will again coarsen 
the grain. 

As we have stated, undisturbed cooling is a condition necessary 
for crystalline growth, a coarse crystalline structure can be partly 
prevented or broken up by vigorous hammering. If this ham- 
mering ceases above the critical range crystallization again sets 
in and the structure is the coarser the higher the temperature 
above the critical point at which the work stops. The finishing 
temperature in working, then, should be for the best results at 
or just above the critical range. 

The question then arises. Why not continue working the steel 
until it is cold? This would be a detriment, inasmuch as the 
grain structure is formed in the critical range and "cold working " 
causes distortions and strains to set up in the grain which result 
in decreased ductility and even brittleness. This effect is more 
pronounced the lower the temperature below the critical point 
at which the steel is worked. Mechanical working provides a 
means to shape steel to form by forging, refines the grain size 
and tends to increase the density of steel decidedly more than 
the steel possessed originally from the mills, where rolled. 

High-grade steels are hammered at the mills into bars and 
rolled to proper size. 

It will be seen from the following illustrations what is meant 
by mechanical working and the effect it has in the grain structure. 

It is of course difficult to show this effect by means of micro- 
photograph, so the pen is resorted to as a means of explaining 
the points more clearly. 

Fig. 5 shows the grain of steel in the ingot, forgetting for the 
time the possible conditions entering in steel in this form, such 
as segregations, pipes, etc. The illustration is just a cross section 
before working of a low carbon forging steel. The subsequent 
illustrations are self explanatory, namely Fig. 6 shows the ingot 
rolled or hammered, and the reduction in size of grain is seen. 



STEEL AND ITS TREATMENT 



11 




Fig. 5 
Ingot of Steel 






Fig. 6 
Rolled and Hammered 










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Fig. 7 
Light Blows 











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Fig. 9 
Properly Hardened 




Fig. 11 

Restored by Hammering 

or Heat Treatment 



Fig. 7 shows the eflfect of improper working, the result of 
light blows on the surface, which do not extend their reducing 



12 STEEL AND ITS TREATMENT 

force to the center; but this is remedied by anneaHng, Fig. 8, 
which promotes the adjustment of the grains and reUeves the 
strains in working. The steel is now in a condition to be properly 
hardened, and a fine, even, silky grain is the result if the proper 
temperature and bath have been used in hardening. Fig. 9. If 
too high temperature is used in hardening a coarse crystaUine 
formation appears. Fig. 10, which can only be restored, provided 
the piece permits, by working or hammering and proper heat 
treatment afterward, Fig. 11. 

Annealing 

Inasmuch as the anneaHng process has an important bearing 
upon its physical properties, its mechanical treatment and its 
subsequent effect on the heat treatment of steel after machining, 
it is essential that the basic principles of this operation be thor- 
oughly understood. 

The purpose of annealing steel is, 1st, To increase its softness 
and ductility and facilitate subsequent machining operations; 
2d, To remove existing coarseness of grain and secure a de- 
sirable combination of strength, elasticity and ductility for the 
resisting of strains; and 3d, To relieve internal stresses, such 
as are induced by forging, rolling or by non-uniform contrac-. 
tion in cooling. 

These changes of physical properties are due to the changes 
of structure caused by the heating operation, which operation 
consists essentially of three parts: 1st, Heating the steel to the 
desired temperature; 2d, Holding at the temperature until 
the steel is thoroughly heated; 3d, Cooling. 

Since all crystallization is obliterated in heating steel through 
the critical range, it is necessary then to heat the steel through 
this range as the first step in the annealing operation. Heating 
to a temperature below the critical range would induce no struc- 
tural change whatever, but should you heat considerably above 



STEEL AND ITS TREATMENT 13 

the range you would again bring about a form of crystallization, 
which is detrimental. 

The following ranges of temperatures are recommended by 
the Committee on Heat Treatment of the American Society of 
Testing Materials. They also state that for steels of a Man- 
ganese Content greater than .75 % slightly lower temperatures 
are advisable. 

Range of Carbon Content Range of Annealing Temperature 

Less than 0.12 per cent 875° to 925° C. (1587° to 1697° F.) 

.12 to .29 per cent 840° to 870° C. (1544° to 1598° F.) 

.30 to .49 per cent 815° to 840° C. (1499° to 1544° F.) 

.50 to 1.00 per cent 790° to 815° C. (1454° to 1499° F.) 

The time at which the steel should be held at an annealing 
heat is governed largely by the size of the piece. In order to 
bring the interior of large objects to an effective annealing tem- 
perature the outside may often be heated advantageously some- 
what above the desired temperature. Therefore a range of 
temperatures is given for each range of carbon content. 

The upper limit of this range applies to larger objects and also 
to the lower range of carbon content given. 

The rate of cooling should be regulated to suit the carbon 
content of the steel and the physical properties desired. The 
higher the carbon the slower the cooling. Also the slower the 
cooling the softer and more ductile the steel and lower will be 
the elastic limit and tensile strength. Steel containing more 
than .50 % carbon should cool slowly either in the furnace, lime 
or clay until it becomes black in color, when it may be re- 
moved. In case great softness and ductility is desired all steels 
should be subjected to slow cooling. 

It is desired, of course, to have some definite range of tem- 
peratures to control the elasticity and ductility of the steel. 

For very high elastic limit and tensile strength heat to 500° 
to 650° C. (932° to 1202° Fahr.). In this case the ductility will 



14 STEEL AND ITS TREATMENT 

be low. Some steels, such as watch springs and shaftings, are 
annealed at 350° C. (662° Fahr.). Very little commercial anneal- 
ing is done below 500° C. (932° Fahr.). 

For intermediate tensile strength, elastic limit and ductility 
best suited for the majority of cases, anneal at 600° to 650° C. 
(1112° to 1202° Fahr.). 

For the greatest ductility with good strength and elastic limit, 
anneal at 725° to 750° C. (1337° to 1382° Fahr.). 

Internal stresses caused by forging or rolling are partially 
eliminated by heating steel to a temperature of 538° to 649° C. 
(1000° to 1200° Fahr.) and allowing to cool slowly. 

The control of the annealing operation by definite heats and 
methods unquestionably prepares steel to respond better to 
hardening and treating, reduces the strains and distortions which 
are inevitable and paves the way for a most uniform finished 
product. 

It is advisable to anneal high carbon steel by packing with 
finely ground charcoal in iron boxes and insert the fire end of 
the pyrometer inside of the boxes to assure that the pieces are 
heated to the proper annealing temperature and to obtain a 
check on the heat in the pot. 

Physical Properties 

The industrial importance of heat treatment is to make steel 
possess certain physical properties to best suit the specific pur- 
pose for which the steel is to be used. Whether the greatest hard- 
ness or the greatest softness in a piece of steel is desired, each 
is at the call of the hardener. The effect of the additional ele- 
ments which we know steel to contain and their effect on the 
temperatures used in treating will be considered under a different 
heading. For the present, we will consider only those physical 
properties as are generally specified; namely, tensile strength 
and hardness values, together with a brief sketch of the manner 



STEEL AND ITS TREATMENT 15 

of testing and securing comparative readings in definite units 
and their aid in controlling the production of large quantities 
of machine parts of uniform physical properties. 

Tensile Strength 

In referring to the tensile strength of steel, one usually implies 
those properties of the material known as the Yield Point, which 
is commercially called the Elastic Limit; the Ultimate Strength; 
the Elongation, and the Reduction of Area. 

A "Stress" is an internal force that resists the change in shape 
and size of any material by an applied force, and when the applied 
forces have reached their final values, the internal stresses hold 
them in equilibrium. The simplest case is that of a rope, at each 
end of which a man pulls with a force, say 25 pounds; then in 
every section of the rope there exists a stress of 25 pounds. 
Stresses are measured by the same units as those used for the 
applied forces, and generally in pounds. 

A "Bar" is a prismatic body having the same size throughout 
its length. If a plane is passed normal to the bar, its intersection 
with the prism is called the "cross section" or the "section" of 
the bar, and the area of this cross section is called the "section 
area." 

A "Unit Stress" is the stress on the unit of the section area, 
and this is usually expressed in pounds per square inch. For 
example: Let a bar 2 inches square be subjected to a pull of 
4000 pounds; the resisting stress is 4000 pounds and the unit 
stress is 4000 pounds divided by the area of the bar, which is 4 
inches, or 1000 pounds per square inch. When external forces 
act upon the ends of a bar, in a direction away from its ends, 
they are called "Tensile Forces." When they act towards the 
end they are called "Compressive Forces." A pull is a Tensile 
Force and a push is a Compressive Force, and these two cases 
are frequently called "Tension" and "Compression." The 



16 STEEL AND ITS TREATMENT 

resisting stresses receive similar designations. A Tensile Stress 
is that which resists tensile force. A Compressive Stress is that 
which resists compressive force. 

The terms "Axial Forces" and "Axial Stresses" are used to 
include both tension and compression acting upon a bar along 
the axis of the bar. The first effect of axial load is to change 
the length of the bar upon which it acts. The deformation of a 
bar which occurs in tension is called the "Elongation," and that 
which occurs in compression is called "Shortening." 

When a bar is subjected to a gradually increasing tension the 
bar elongates and up to a certain limit it is found that the elonga- 
tion is proportional to the load. Thus when a bar of wrought 
iron one square inch in section area and 100 inches long is sub- 
jected to a load of 5000 pounds, it is found to elongate closely 
0.02 inch; when 10,000 pounds are applied the elongation is 
0.04 inch; when 15,000 pounds are applied the elongation is 0.06 
inch; at 20,000 pounds, the elongation is 0.08 inch; at 25,000 
pounds the elongation is 0.10 inch. Thus far each addition of 
5000 pounds has produced an additional elongation of 0.02 inch, 
but when the next 5000 pounds are added, making a total of 
30,000 pounds, it is found that the total elongation is about 0.50 
inch, and hence the elongations are increasing in a faster ratio 
than the applied loads and the resisting stresses. 

The "Elastic Limit" is defined as that unit stress at which 
the deformation begins to increase in a faster ratio than the 
applied load. In the above example this Hmit is about 25,000 
pounds per square inch, and this is the average value of the 
elastic limit of wrought iron. 

When the unit stress in a bar is not greater than the elastic 
limit, the bar returns on the removal of the load to its original 
length. Thus the above wrought iron bar was 100.10 inches 
long under the load of 25,000 pounds, and on the removal of the 
load it returned to its original length of 100 inches. When the 
unit stress is greater than the elastic limit, the bar does not fully 



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STEEL AND ITS TREATMENT 17 

return to its original length, but there remains a so-called "Per- 
manent Set." For instance, let the length of the above bar 
under a stress of 34,000 pounds be 102 inches, and on the removal 
of the tension let its length be 101>^ inches. Then the per- 
manent set of the bar is 1^ inches. 

The term "Ultimate Strength " is used to designate the highest 
unit stress that the bar can sustain, this occurring at or just 
before rupture. 

The "Yield Point" is defined to be the unit stress at which 
the deformation increases without any increase in applied load, 
or in internal stress. In commercial testing, the yield point is 
usually called the elastic limit, because the former is more easily 
ascertained than the latter. 

The "Ultimate Elongation" of a bar is determined by making 
two marks upon it before it is subjected to tension, and measuring 
the distance between them before and after the test. The differ- 
ence between these lengths divided by the original length gives 
the ultimate elongation per unit of length. For example: If the 
distance between the two marks is 2 inches and if it becomes 
2.60 inches after the rupture then the total elongation is 0.60 
inch in two inches and the ultimate unit elongation is 0.30 inch, 
or 30%. 

An elongation of a bar is always accompanied by a reduction 
in the area of its cross section. The term "Reduction of Area" 
refers to a ruptured specimen, and means the diminution in sec- 
tion area per unit of original area. Thus, if the original area of 
a specimen is 0.200 square inch, and the area of the ruptured 
section is 0.080 square inch, then the reduction of area is 0.120 
square inch, which when divided by the original area gives 0.60 
or 60%. The reduction of area is an index of the ductility of 
the material, and is generally regarded as a more reliable index 
than elongation, because the ultimate unit elongation is subject 
to variations with the ratio of the length of the specimen to its 
diameter, whereas the reduction of area is more constant. 



18 STEEL AND ITS TREATMENT 

A "Tensile Test" of a vertical bar may be made by fastening 
its upper end firmly with clamps and then applying successive 
loads to its lower end. The elongations of the bar are found to 
increase proportionately to the loads, and hence also to the 
internal tensile stresses, until the elastic limit of the material 
is reached. After the unit stress has exceeded the elastic limit 
the elongation increases more rapidly than the loads. On soft 
material one will note a marked elongation at the yield point 
and on a testing machine this is usually accompanied by a so- 
called "Dropping of the Beam." Elongation is accompanied by 
a reduction of area of the cross section of the bar. Finally the 
ultimate strength of the bar is reached and it breaks. The load 
at the elastic limit, or yield point, which as mentioned above is 
commonly accepted as the commerical elastic limit, divided by 
the original section area gives the unit stress; the load which 
produced the ultimate strength of the bar when divided by the 
original section area gives the ultimate unit stress. The last 
calculation is not theoretically correct, but is used in testing the 
strength of the material. The elongation and reduction of area 
are then measured and calculated as mentioned above ; thereby 
one determines the tensile test values of the bar. 

Methods of Testing the Hardness of Metals 

What property in iron and steel is of more importance than 
that of hardness? In some cases, as with a cutting tool or a 
punching die, the metal is practically valueless unless ;t can 
retain a sharp edge, while in other instances where the material 
has to be machined or cut and trued to shape, even a relatively 
slight increase of hardness is the cause of much inconvenience 
and expense. In a third class of material a good wearing surface 
is of prime importance, while lastly hardness may often serve as 
an indication of a degree of brittleness and untrustworthiness 
which might perhaps be otherwise unsuspected. 



STEEL AND ITS TREATMENT 19 

Hardness may be defined as the property of resisting pene- 
tration or abrasion, and conversely a hard body is one which, 
under suitable conditions, readily penetrates a softer material. 
There are, however, in metals, various kinds of manifestations 
of hardness according to the form of stress to which the metal 
may be subjected. These include tensile hardness, cutting 
hardness, abrasion hardness and elastic hardness. The usual 
quantitative tests for hardness are static in character, but the 
conditions are profoundly modified when the penetrating body 
is moving with greater or less velocity. The resistance to the 
action of running water, to the effect of a sandblast, or to the 
results of the pounding of a heavy locomotive on a steel rail, 
afford examples of what might perhaps for purposes of dis- 
tinction be called dynamic hardness. 

Four typical methods of measuring hardness include the 
sclerometer, introduced by Turner; the scleroscope, invented by 
Shore; the form of indentation test adopted by Brinell, and the 
drill test introduced by Keep. The principles underlying the 
four methods selected for comparison may be briefly described 
as follows: 

Turner's Sclerometer 

In this form of test a weighted diamond point is drawn once 
forward and once backward over the smooth surface of the 
material to be tested. The hardness number is the weight in 
grammes required to produce a standard scratch. The scratch 
selected is one which is just visible to the naked eye as a dark 
line on a bright reflecting surface. It is also the scratch which 
can just be felt with the edge of a quill when the latter is drawn 
over the smooth surface at right angles to a series of such scratches 
produced by regularly increasing weight. 



20 STEEL AND ITS TREATMENT 

Shore's Scleroscope 

In this instrument a small cylinder of steel, with a diamond 
point enclosed in a glass tube with graduations of arbitrary 
units, is allowed to fall upon the smooth surface of the material 
to be tested. The hardness number is the height of the rebound 
of the hammer. The hammer weighs slightly over two grammes. 
The height of the rebound of hardened steel is in the neighbor- 
hood of 100 on the scale, or about 160 millimeters, while the 
total fall is about 10 inches, or 225 millimeters. 

Brinell's Test 

This method is founded upon the effect produced on a sub- 
stance by a known load pressing through a spherical ball into 
the surface of the material to be tested. The hardness numbers 
are found by the use of certain factors and coefficients ; they are 
evidently not intended to represent actual degrees of hardness 
relatively to the hardest substance known (probably a diamond), 
but only convenient, comparable units, indicating sufficiently, 
different conditions in the materials tested, they are taken from 
practical experience rather than from scientific knowledge. 

The method of working is as follows: The weight or load given 
in kilograms is generally 3000 for iron and steel and 500 for softer 
metals and alloys. The pressure is applied hydraulically by 
means of an oil pump and is transmitted through the plunger 
to a hardened-steel ball, which makes a cup-shaped impression 
on the test piece. From the diameter of this impression and the 
load, a working formula has been deduced, and a table of hard- 
ness numbers computed. 

The formula is as follows: 

3000 
H 



~{D — ^D^—d'^) 



STEEL AND ITS TREATMENT 21 

where 

^=:^Hardness; 

Z)==Diameter of ball (10 millimeters); 
f/=^ Diameter of impression. 

The diameter of the impression is read off by means of a 
microscope, having a micrometer scale, graduated in tenths of 
a millimeter, contained in the diaphragm of the eye-piece. A 
verifying scale is supplied with the microscope. 

Example: Let the diameter of impression^=4.7 mm., then 

^ 3000 

£1 



31.416 



(10 — y/ 100 — 22.09) 



disregarding further decimal points 
3000 250 



15.708 X 1.17 1.309 X 1.17 



163 hardness No. 



This formula is not quite accurate, since it does not take into 
consideration the mass of material displaced but only the super- 
ficial area of the impression, yet is perhaps the simplest working 
formula. 

Keep's Test 

In this form of apparatus a standard steel drill is caused to 
make a definite number of revolutions while it is pressed with 
a standard force against the specimen to be tested. The hardness 
is automatically recorded on a diagram on which a dead soft 
material gives a horizontal line, while a material as hard as the 
drill itself gives a vertical line, intermediate hardness being 
represented by the corresponding angle between and 90 degrees. 



22 STEEL AND ITS TREATMENT 

Each form of test has its advantages and its Umitations. The 
sclero meter is cheap, portable and easily applied, but it is not 
applicable to materials which do not possess a fairly smooth 
reflecting surface, and the standard scratch is only definitely 
recognized after some experience. The Shore test is simple, rapid 
and definite for materials for which it is suited. As shown by 
De Freminville, the result obtained varies somewhat with the 
size and thickness of the samples, while if the test piece is sup- 
ported on a soft material, such as plasticine, the results are value- 
less. It should also be pointed out that India-rubber gives a 
rebound of 23, which is equal to that of mild steel, while light 
soft pine wood gives a rebound of 40, which is nearly twice as 
great as that of gray cast iron. Curiously enough, hard wood, 
like teak wood, gives a rebound of about 12, while some samples 
are considerably less than this. As illustrating the influence of 
the support, a sample of exceptionally hard rolled copper about 
^/^5 inch in thickness, when supported on a block of hard steel 
and tested with the blunt or ''Magnified" hammer, supplied 
with the apparatus, gives a value of 30, which was increased 
to 34 when the copper was supported on wood. A sample of 
brass gave only a value of 17, and yet this brass would scratch 
the copper while the copper would not scratch the brass. From 
these results it is evident that the Shore test is applicable only 
to a certain class of substances. It appears to test what may 
be termed to "elastic hardness" and gives high results with 
metals in the "worked hard" condition. Tests appear to show 
that good results however are obtained with glass and with 
porcelain as well of course as with most metals. 

The Brinell test is especially useful for constructive material. 
It is easily applied and definite and is the hardness test most 
generally employed ; it cannot be applied to very brittle materials, 
such as glass or hard minerals. 

A very important question arises in connection with these 
various tests; namely, as to whether there is any observed 



STEEL AND ITS TREATMENT 



23 



agreement between the results which are arrived at by such 
entirely different methods. It will be noticed that in each case 
an arbitrary scale is adopted. If the weight used on the sclerom- 
eter had been ounces instead of grammes the hardness numbers 
would naturally have been difTerent. Similarly Brinell's test 
might have been expressed in tons and inches, or a definite weight 
of hammer and height of scale adopted by Shore. Hence, all 
that can be expected is a proportionality in the results, and if 
this is ascertained it should be possible to convert values on one 
scale into results on another. In the following table will be 
found a comparison of hardness values of various materials. 
For the purpose of comparison, the actual Brinell hardness values 
have been divided by 6. The sclerometer and scleroscope values 
are actual readings. It appears, from a study of the table, that 
all the instruments with simple homogeneous substances give 
results which are either in actual agreement with or proportional 
to the results obtained by the other form of apparatus. 



Metals 


Sclerom- 
eter 


Sclero- 
scope 


Brinell 


Lead 


1.0 

2.5 
6.0 
8.0 

15^0 

21.0 

21-24 

24.0 

36.0 

72.0 


1.0 

3.0 

7.0 

8.0 

12.0 

22^0 
24.0 
27.0 
40.0 
70.0 
95.0 


1 


Tin 


2 5 


Zinc 


7 5 


Copper (soft) 

Copper (hard) 

Softest Iron 

Mild Steel 

Soft Cast Iron 


12.0 
14.5 
16.24 
24 


Rail Steel 

Hard Cast Iron 


26-35 
35.0 


Hard White Iron 


75 


Hardened Steel 


93.0 



24 



STEEL AND ITS TREATMENT 



Table of Brinell Hardness Numbers and Estimated Tensile Strength 
FOR 3000 Kilogram Pressure on a 10 m/m Ball Testing Machine 



Dia. of 


Hard- 


Ulti- 


1 
Dia. of 


Hard- 


Ulti- 


Dia. of 


Hard- 


Ulti- 


Dia. of 


Hard- 


Ulti- 


Im- 
pres- 


ness 
Nu- 


mate 
pounds 


Im- 
pres- 


ness 
Nu- 


mate 
pounds 


Im- 
pres- 


ness 
Nu- 


mate 
pounds 


Im- 
pres- 


ness 
Nu- 


mate 
pounds 


sion in 


meral 


persq. 


sion in 


meral 


per sq. 


sion in 


meral 


per sq. 


sion in 


meral 


per sq. 


m/m 




in. 


m/m- 




in. 


m/m 




in. 


m/m 




in. 


2.00 


946 


465,100 


3.00 


418 


204,100 


4.00 


228 


112,600 


5.00 


143 


70,200 


2.05 


898 


442.100 


3.05 


402 


197,300 


4.05 


223 


109,700 


5.05 


140 


68,700 


2.10 


857 


421.600 


3.10 


387 


190,800 


4.10 


217 


106,900 


5.10 


137 


67,200 


2.15 


817 


402,000 


3.15 


375 


184,600 


4.15 


212 


104,200 


5.15 


134 


65,800 


2.20 


782 


383.700 


3.20 


364 


178.800 


4.20 


207 


101,600 


5.20 


131 


64,500 


2.25 


744 


366,600 


3.25 


351 


173,200 


4.25 


202 


99.100 


5.25 


128 


63,100 


2.30 


713 


350,600 


3.30 


340 


167,800 


4.30 


196 


96,700 


5.30 


126 


61.800 


2.35 


683 


335,700 


3.35 


332 


162,700 


4.35 


192 


94,400 


5.35 


124 


60,600 


2.40 


652 


321,600 


3.40 


321 


157,800 


4.40 


187 


92,200 


5.40 


121 


59.400 


2.45 


627 


308,400 


3.45 


311 


153,100 


4.45 


183 


90,000 


5.45 


118 


58.200 


2.50 


600 


295,900 


3.50 


302 


148.600 


4.50 


179 


87,900 


5.50 


116 


57.000 


2.55 


578 


284,300 


3.55 


293 


144,300 


4.55 


174 


85,800 


5.55 


114 


55.900 


2.60 


555 


273.300 


3.60 


286 


140,200 


4.60 


170 


83,900 


5.60 


112 


54,800 


2.65 


532 


262,900 


3.65 


277 


136,200 


4.65 


166 


82,000 


5.65 


109 


53,700 


2.70 


512 


253,100 


3.70 


269 


132,400 


4.70 


163 


80,100 


5.70 


107 


52,700 


2.75 


495 


243,800 


3.75 


262 


128,800 


4.75 


159 


78,300 


5.75 


105 


51,700 


2.80 


477 


235,000 


3.80 


255 


125,300 


4.80 


156 


76,600 


5.80 


103 


50,700 


2.85 


460 


226,600 


3.85 


248 


121,900 


4.85 


153 


74,900 


5.85 


101 


49,700 


2.90 


444 


218,700 


3.90 


241 


118,700 


4.90 


149 


73,300 


5.90 


99 


48,800 


2.95 


430 


211,200 


3.95 


235 


115,500 


4.95 


146 


71.700 


5.95 


■ 97 


47,900 



Pressure 



Hardness Number 



Area of Impression 
Tensile in Kg. per sq. m/m = coefficient .346 x hardness number 
1422.3 Factor to convert Klg. per sq. m/m to lbs. per sq. in. 



Pyrometers 

In the heat treatment of steel too great emphasis cannot be 
laid upon the controlling and regulating of the temperature of 
heating, whether it be for hardening, drawing or annealing. The 
values of all experiments are rated according to their accuracy, 
and in the treatment of steels where the critical changes must be 
determined and the furnace regulated to the predetermined heat 
we are forced to depend on the pyrometer for all heats over 543° 
C. (900° Fahr.) and the thermometer for all temperatures below 
543° C. (900° Fahr.). 



STEEL AND ITS TREATMENT 25 

Inasmuch as the critical changes of the steel are above 543° C. 
(900° Fahr.) for hardening or treatment, the pyrometer assumes 
a position of importance in a treatise on steel and its relation to 
the industries. 

One of the difficulties connected with the careful regulation 
of the temperature of furnaces was formerly the lack of a pyrom- 
eter which would record over any required time the variations 
in temperature and so enable them to be controlled. But today 
there are a number of reliable commercial pyrometers on the 
market, with the use of which, under proper working conditions, 
many and usually the greatest difficulties in the heat treatment 
of steel can be overcome. 

In the heat treatment of steel the types of pyrometers most 
generally used are the thermo-electric pyrometers, resistance 
pyrometers and optical pyrometers. Of these three the thermo- 
electric method is the most important. 

The theory on which the operation of thermo-electric pyrom- 
eters is based is briefly described as follows : 

If, when two wires of different composition are joined together 
at both ends so as to make a complete circuit, one of these junc- 
tions be at a different temperature from the other, a dilTerence 
of electrical potential is set up at the junctions and an electric 
current flows through the wires. Such a pair of wires is called 
a thermo-electric couple. If the wires are of uniform composition 
the potential difference depends upon the difference of tempera- 
ture alone, and the strength of the current will vary directly as 
the differences of temperature. If a galvanometer be inserted 
in the circuit, this current can be measured, and if the current 
corresponding to various differences of temperature be once 
ascertained, the apparatus can be used as a means of measuring 
temperature. The thermo-electric couples are divided into two 
principal classes: Base Metal and Noble Metal couples. 

There appears to be an insistent demand on the part of many 
in charge of technical processes requiring temperature control for 



26 STEEL AND ITS TREATMENT 

inexpensive and robust measuring apparatus. For this reason, 
if for no other, the use of the base metal couple has become firmly 
established and its success lies principally in the production of 
fairly satisfactory alloys of high electro-motive-force with tem- 
perature changes, which can be made into strong, practically 
unbreakable, thermo-couples, and the development of an inex- 
pensive fairly robust millivoltmeter. Examples of this type of 
couple are pure iron as one wire and a constant as the other, or 
nickel as one wire and iron as the other, while an example of a 
noble metal couple is a couple made up of platinum as one wire 
and platinum plus 10% rhodium as the other. 

When, in the case of the use of alloys or metals such as the 
above, possessing critical regions, or regions of molecular trans- 
formation, their rate of heating or cooling is varied, the electro- 
motive-force readings of the couples will not in general be the 
same for a given temperature within this range. In some cases, 
especially for wires or rods of considerable diameter, the electro- 
motive-force temperature relations may be changed at all tem- 
peratures below this region as well, due to the retardation or 
partial prevention of the complete transformation by chilling. 
Re-annealing and slow cooling will oftentimes restore the original 
annealed condition. It is therefore important to frequently check 
and calibrate a base metal thermo-couple. 

The noble metal couple has its advantages. It possesses a 
fairly linear temperature electro-motive-force relation, especially 
so between 300° and 1100° C. (572° and 2012° Fahr.). It can be 
used at temperatures as high as 1500° C. (2700° Fahr.) with 
great accuracy. It is but sUghtly alterable, can be obtained 
in a homogeneous condition, so that depth of immersion in the 
furnace or heating medium brings about little or no error, and 
on account of its being used in connection with a high resist- 
ance galvanometer, errors due to changes in line or lead resist- 
ance and that of the couple itself are practically negligible. 

Heating pyrometer couples to high temperatures in a reducing 
atmosphere causes an alteration of the elements. 



STEEL AND ITS TREATMENT 27 

It is thus indispensable to protect the couples against any re- 
ducing atmosphere. The two leads should be insulated from one 
another throughout their length ; for this, use may be made of 
porcelain pipe stems or a thread of pure asbestos wound about 
each wire. This is a convenient method of insulation for labora- 
tory use, although ordinary asbestos is likely to contain impurities 
which will damage the couple. With this arrangement it is im- 
possible to go above 1200° to 1300° C. (2192° to 2372° Fahr.), 
at which temperature asbestos melts. An iron tube can be used 
for protection if the temperature does not exceed 800° C. (1472° 
Fahr.), in the lead bath serving to hardened steel for example, 
and for movable couples which are exposed to heat only during 
the time necessary to take the observation. In all cases where 
the furnace whose temperature it is desired to measure is under 
reduced pressure, suitable precautions must be taken to prevent 
any permanent entrance of cold air by the orifice necessary for 
the introduction of the tube as well before as during an obser- 
vation. Otherwise, one runs a chance of having inexact results. 

In the case of prolonged observations in a reducing atmosphere 
or in contact with melted bodies, the couples should be protected 
by enclosing in a covering impermeable to the melted metals 
and to vapors. 

Whether the couples be made of base or noble metal, for good, 
accurate service the wire should be well insulated and the junc- 
tion of the elements protected from the gases of the furnace, the 
cold-end junction kept fairly constant, the accuracy of the system 
checked or calibrated frequently, depending on the temperature 
and length of time in service (for checking, a standard galvanom- 
eter and couple is often set aside and used only for the above 
purpose) and the entire system handled with care, for in the 
majority of cases errors and false readings as well as lack of 
confidence in the pyrometer is caused by the abuse or wrong use 
of the apparatus. 



28 STEEL AND ITS TREATMENT 

Classification of Steel 

Steels are commonly divided in two classes — Straight carbon 
steels and special steels, or steel alloys. The former differ from 
the latter in that they are made up almost entirely of iron com- 
bined with more or less carbon and containing small amounts of 
such elements as manganese, sulphur, phosphorus, silicon, while 
the special steels result from mixing the above with nickel, 
chromium and vanadium. 

Straight Carbon Steels 

Steels are generally graded according to the amount of carbon 
they contain. The following terms are those most commonly 
used: 

Very low Carbon steel, very mild or extra mild steel; 

Very soft, dead soft steel — Carbon not over 0.10 per cent.; 

Low Carbon Steel, mild steel, soft steel — ^Carbon not over 
0.25 per cent.; 

Medium high Carbon Steel — Carbon 0.26 to 0.60 per cent.; 

High Carbon Steel, hard steel — Carbon over 0.60 per cent.; 

Very high Carbon Steel, extra hard steel — Carbon over 1.25 
per cent. 

This classification is somewhat arbitrary, as there are no sharp 
lines in the carbon percentages of separation universally recog- 
nized between the various grades. 

Steel containing about 0.85 per cent, carbon is also known as 
"Eutectoid" steel, that containing less carbon as ''Hydro- 
Eutectoid" steel, and more highly carburized metal as "Hyper- 
Eutectoid" steel. 

Very Low Carbon Steels 

If one should study the rate of cooling of a sample of steel 
containing some 0.10 per cent, carbon, from a high temperature. 



STEEL AND ITS TREATMENT 29 

three thermal retardations would be detected: Avs, at about 
850° C. (1562° Fahr.); Avj near 750° C. (1382° Fahr.), and 
Ari about 675° C. (1247° Fahr.). Of these three critical points 
the At 3 would be the most marked, while Ar2 and Ari would be 
faint. On heating, corresponding retardations will occur, due 
to spontaneous absorption of heat, the critical points being 
designated as Ac3, Ac2 and Aci. Of these, Acs and Aci will occur 
at temperatures some 25° C. or more higher than Ar3 and Ar^ 
while Ac2 will be nearly the same as Ar2; that is about 750° C. 
(1382° Fahr.). 

The point A2 is generally less marked than the points A3 
and Ai, and unHke A3, its position is little affected by the carbon 
content, and unlike A3 and Ai the point on heating Ac2 occurs 
at nearly the same temperature as the point on cooling Ar2. 
It also appears to cover a wide range of temperatures. 

Thermal Critical Points of a Medium High Carbon 

Steel 

The cooling of a steel containing about .45% carbon reveals 
the existence of tv/o critical points: One, evidently the point 
of recalescence, Ari, at the usual temperature 650°C. (1202° 
Fahr.) to 700° C. (1292° Fahr.) and one upper point around 
775° C. (1427° Fahr.). It is generally assumed that the two 
upper points have united to form a single one, and is desig- 
nated accordingly by Ar3,2. Increasing the carbon content 
decreased the interval of temperature between the two upper 
points, until finally for a certain carbon content the points meet 
to form the double point Ar3,2. This appears to occur at about 
0.40% carbon. 

Thermal Critical Points of Eutectoid Steel 

Eutectoid Steel, that is a steel containing about 0.85% 
carbon, exhibits but one critical point, the point of reca- 



30 STEEL AND ITS TREATMENT 

lescence, very marked at about 675° C. (1247° Fahr.) on cooling. 
The view generally held concerning this merging is that increasing 
the amount of carbon has so depressed the position of the two 
upper points as to cause them to unite with the lower point, 
forming a triple point to be designated as Ar3,2,i. The critical 
point* on heating is designated by Ac3,2,i. 

What is meant by Eutectoid Steel? It has been mentioned 
above that steel is made up of so-called minerals. For an example : 
0.30% carbon is composed of about 35.3% Pearlite and 64.7% 
Ferrite. As the carbon content increases to, say, .50%, the 
structural composition is about 41.8% Ferrite and 58.2% 
Pearlite. Thus, the quantity of Pearlite increases while the 
Ferrite decreases up to about 0.85% carbon, where it is 
exclusively Pearlite. Such a steel is quite universally called 
"Eutectoid Steel," but had formerly been called "Saturated 
Steel." Steel containing more than 0.85% carbon (Hyper- 
Eutectoid Steel) contains what is called "Free Cementite," 
which is structureless, possesses a metallic lustre and is extremely 
hard. Thus, a 1.25% carbon will contain about 93% Pearlite 
and 7% Free Cementite. 

Thermal Critical Points of Hyper-Eutectoid Steel 

When a sample of steel containing a decided amount of free 
Cementite is cooled from a high temperature, an upper critical 
point is detected, at which point the Cementite is liberated from, 
solution. This point is designated by Acm, Ar cm on cooling 
and Ac cm on heating, "cm" standing for Cementite. The 
position of the point Acm is lower as the proportion of car- 
bon decreases, finally merging with the point A3, 2,1 at the 
Eutectoid point. 

The following table shows some critical point determinations 
on cooling Straight Carbon Steels of the carbon content indicated. 



STEEL AND ITS TREATMENT 



31 



Carbon 
Per Cent. 


Arcm 
Begin. 


Ar 3 
Begin. 


Max. 


Ar2 
Begin. 


Max. 


Ar 1 
Begin. 


Max. 


Ar 
Begin. 


.01 
.12 
.24 
.38 
.53 
.80 
.93 
1.30 


883° C. 


901° C. 
894° C. 
890° C. 

774° C. 
774° C. 


900° C. 
838° C. 
Merged 

Merged 


784° C. 
774° C. 

778° C. 
762° C. 


762° C. 
762° C. 
762° C. 
762° C. 
730° C. 

Merged 


693°' C. 

696° C. 
700° C. 

Merged 


688° C. 
693° C. 
699° C. 
700° C. 
695° C. 
699° C. 
695° C. 


616° C. 
600° C. 
611° C. 

617° C. 

587° C. 
600° C. 



Effect of the Elements in Steel 

The elements that combine to make steel, their relation to 
one another, their effect when the percentages of one or more 
are changed which add or take away certain physical properties 
of the steel, and their action under heat, offer a field of research 
work that cannot be covered in this treatise. However, it may 
be well to give the general characteristics of these, elements as 
they manifest themselves in the heat treatment and establish a 
relation between the chemical analysis of steel and the effect of 
these elements on the final product. 



Carbon 

The general influence of carbon in steel is to give greater 
tenacity. It also renders the steel susceptible to hardening. 
The tensile strength is increased about 600 to 800 pounds per 
square inch for each additional point of carbon, while the ductility 
is decreased about 0.5 per cent, for each additional point of 
carbon. Steel with 0.20 per cent, carbon begins to show ap- 
preciable hardening when cooled quickly, but does not show 
evidence of brittleness in the normal state until the carbon has 
reached approximately 0.70 per cent. The general effect and 
position of carbon in steel has never been fully determined. For 



32 STEEL AND ITS TREATMENT 

the most part the tables and treatments, together with the phys- 
ical properties that are mentioned later on, are the best indica- 
tions of the properties of carbon and its relation to steel and the 
other elements. 

Manganese 

Manganese is an element always found in steels, but its true 
properties and effects were not known until about twenty years 
ago, when they were discovered by R. A. Hatfield, a metallurgist 
and steelmaker of Sheffield, England. 

When more than 2 per cent, and less than 6 per cent, of man- 
ganese is added, with the carbon less than 0.5 per cent., it makes 
steel very brittle, so that it can be powdered under the hand 
hammer. From 6 per cent, of manganese up this brittleness 
gradually disappears until 12 per cent, is reached, when the 
former strength returns and reaches its maximum at about 14 
per cent. After this, a decrease in toughness, but not in trans- 
verse strength, takes place until 20 per cent, is reached, after 
which a rapid decrease again occurs. 

Steel with from 12 to 15 per cent, of manganese and about 
1.25 per cent, of carbon is very hard and cannot be machined or 
drilled in the ordinary way; yet it is so tough that it can be 
twisted and bent into peculiar shapes without breaking. 

Manganese in the form of a ferro compound containing about 
80 per cent, of manganese is added to steel at the time of tapping, 
so that it may seize the oxygen, which is dissolved in the bath, 
and transfer it to the slag as oxide of manganese. Manganese 
prevents the coarse crystallization which the impurities would 
otherwise induce, and steels low in phosphorus and sulphur 
require less manganese than those having comparatively high 
percentages. 

The maximum temperature to which it is safe to heat steel, 
both in its manufacture and subsequent treatment, is raised by 



STEEL AND ITS TREATMENT 33 

manganese, owing to its resisting the separation of the crystals 
in cooling and conferring the quahty of hot ductiHty. This 
makes it one of the most valuable factors, in the making of steel, 
if the proper percentages are used. 

Phosphorus 

The impurities, phosphorus and suphur, have been the bane 
of engineers, designers and all users of steel products, and more 
time, more energy and more money have been spent to get rid 
of phosphorus than any other element in steel. It was formerly 
thought that phosphorus up to about 0.12 per cent, strengthened 
steel, but when these same steels were put into actual use they 
failed and the cause was nearly always traced to the phosphorus. 
In the rolling mill, phosphorus does not show any bad effects, 
as the heat under which the steel is worked seems to overcome 
them, but when the metal has cooled and is subjected to sudden 
shock or to vibrational stresses it breaks very easily. The lower 
the temperature and the higher the phosphorus the more brittle 
the steel. This has led to the term "cold shortness," as applied 
to the effect of phosphorus in steel. 

Phosphorus reduces the ductility of steel under a gradually 
applied load, as shown by the reduction of area, elongation and 
elastic ratio when specimens are pulled in the ordinary, static 
strength-testing machine. But when the steel is tested in the 
rotary or alternating vibrational-stressing machine, as well as 
with a pendulum-impact machine, the decrease in ductility and 
toughness is shown to a much greater degree. 

Phosphorus steels are so capricious that they may show a 
reasonably high static ductility and still show very brittle when 
shock tests are applied. 

Therefore, for all steels subjected to strains, or sudden shocks, 
the phosphorus content should be below 0.045 per cent. 



34 STEEL AND ITS TREATMENT 

Sulphur 

Sulphur causes steel to crack, tear and check in rolling, forging, 
heat-treating or hot working, and therefore the term of "hot 
shortness" has been applied to its effect on steel. This effect is 
the opposite to that of phosphorus. 

When steel is heated beyond a dull red heat sulphur will cause 
a crystaUization to take place, and when high temperatures are 
reached the grain becomes very coarse. The sulphur dissociates 
and forms a gas which diffuses between the iron crystals, separat- 
ing them and preventing perfect cohesion. When contraction 
from cooling takes place this may cause microscopic cracks or 
even cracks large enough to be seen by the naked eye. These 
cracks, of course, weaken the metal. It is also the bane of the 
steelmaker, owing to its liability to cause blow holes, pipes and 
seams. 

Since manganese has a great affinity for sulphur these two 
elements when brought together at the high temperature in the 
manufacture of steel combine chemically, forming manganese 
sulphide, which sometimes segregates and collects between the 
crystals of the steel and causes an injurious effect by reducing 
the crystalline cohesion. Hence, the percentage of sulphur in 
steel should be extremely low. It is customary to specify steel 
containing less than 0.05 per cent, sulphur. 

Silicon 

Silicon has a tendency to remove the gases and oxide from 
steel as well as the traces of dissolved oxygen. This prevents 
the formation of blow holes and gives the steel greater toughness. 
Thus it is better able to withstand wear or crushing from con- 
tinual pounding. 

The influence of siHcon on the results of quenching is similar 
to that of carbon in many ways. It is also dependent upon the 
co-existing amount of carbon and manganese. It neutralizes the 



STEEL AND ITS TREATMENT 35 

injurious tendencies of manganese and it is difficult to obtain 
silicon in steel without the presence of manganese. 

Effect of Nickel 

Nickel in steel increases its ductility, toughness, resistance to 
abrasion and shock. It also increases very considerably the ratio 
of the elastic limit to the tensile strength, and renders these steels 
more susceptible to heat treatment. 

Steels contain from 1 to 5% of nickel, according to the desired 
results. 

An addition of 2% nickel to a steel, when properly treated, 
will increase its strength to nearly double that of straight 
carbon steel of the same carbon content. 

Nickel added to ordinary carburizing steel in comparatively 
small percentages obviates the brittleness which is usually pro- 
duced by carburizing and gives more uniform results. 

These steels when properly carburized and heat treated, give 
excellent service in such parts as shafts, ball and roller bearings, 
gears, etc. 

It should be remembered, however, that the mere addition of 
nickel to steel does not guarantee exceptional physical properties, 
which can only be obtained by the most careful and proper heat 
treatment. 

In recent years considerable work has been done on the 
higher nickel steels which give a martensitic structure on air 
cooling. These experiments have been conducted on high carbon, 
high nickel steels, as well as low carbon, high nickel steels car- 
burized. The theory of this process is based on the retaining, 
by the presence of the high nickel content, of the martensitic 
structure on slow cooling, thereby eliminating the quenching 
operation. You will please remember that the martensitic 
structure of ordinary high carbon steel can only be retained by 
rapid cooling, such as quenching. 



36 STEEL AND ITS TREATMENT 

Chromium 

Chromium added to steel increases the elastic limit, hard- 
ness, resistance to shock and alternate stresses. 

It is the most active element in making steel respond to heat 
treatment, giving the penetration of the heat treating the greatest 
depth obtainable with any steel. 

This elernent decreases the tendency of crystalline growth and 
imparts a very fine grain structure. 

In the rolled or forged condition low chromium, in combination 
with low carbon, has practically no effect on the physical proper- 
ties, but it affects materially the results obtained by heat treating 
the same. 

Extreme hardness may be obtained in chromium steels, as the 
chromium intensifies the sensitiveness of the metal to quenching 
and greatly reduces the liability to fracture, which is found in 
carbon steels. 

Chromium steel practically shows no grain or fiber and possesses 
a high power of resistance to shocks. This has made it almost 
universally used for Armor Plate. 

When chromium is combined with nickel or vanadium it 
makes the strongest and best wearing steel on the market, and 
can be machined much more easily than when chromium alone 
is used. Small gears can be made with these alloying materials 
added to steel that if properly heat treated will be so tough and 
strong as to make it almost impossible to break out a tooth, even 
with a sledge hammer. Some of the best grades of chrome nickel 
or chrome vanadium steel contain from 0.75 to 1.50 per cent, of 
chromium. If more than this is used the metal becomes too 
brittle and difficult to retain the high strengths which are given 
with the lower percentages of chromium. The carbon content of 
these steels is also kept comparatively low. A percentage of 0.45 
of carbon makes these steels about as hard as can be cut with 
machine tools, even when thoroughly annealed. Many of these 



STEEL AND ITS TREATMENT 37 

steels contain 0.25 per cent, of carbon, as the chromium gives 
the metal a hardness similar to that of carbon, but one which 
makes the cohesion of the molecules greater. This makes the 
metal more homogeneous and gives it the ability to resist shock 
and torsional stresses. Thus, this alloy is one of the best steels 
for crank shafts of internal-combustion engines or other parts of 
machinery which have to withstand similar vibrational stresses. 
The chrome nickel steels are difficult to forge, as it is dangerous 
to hammer them after the temperature has dropped below that 
which makes the metal a bright yellow. It must be heated 
repeatedly to forge pieces of any size or ^intricate shape. 



Vanadium 

Vanadium has made great strides in the past few years as an 
alloying element and is used in steel castings and cast iron as 
well as in steel mill products. 

Vanadium, when added to steel in percentages up to 2 per 
cent., has a very marked effect upon the physical properties, 
particularly decreasing the susceptibility to sudden shock stresses 
and fatigue. 

Owing to its affinity for oxygen it acts as a cleanser to the 
metal, thereby increasing the molecular cohesion. 

Vanadium also removes nitrogen, which is very detrimental to 
steel, even in infinitesimal quantities. 

Vanadium steel is used largely for crank shafts, connecting 
rods, piston rods, crank pins, gears, saws, gun barrels, springs, 
etc. 

The Thermal or Heat Treatment of Steel 

Scientific heat treatment has developed from the use of the 
high-grade steels. It is upon this treatment that we largely 
depend for the production of the most superior physical properties. 



3S STEEL AND ITS TREATMENT 

The highest priced steel may be so improperly treated that the 
results or properties obtained are far inferior to a well treated, 
cheaper grade of steel. Although these changes, due to the 
thermal treatment, are governed by definite laws it must be 
remembered that the same treatment cannot be appHed to all 
steels with satisfactory results, but that each type of steel responds 
best to its own characteristic temperatures. 

The subject of heat treatment embraces the operations of 
annealing, hardening, carburizing and case-hardening, and the 
tempering or drawing of hardened steels. 

The Hardening of Steel 

The hardening of steel consists of two distinct steps: First, 
heating to the hardening temperature, and second, cooling from 
that temperature. 

If a piece of steel is heated through the critical range a struc- 
tural change takes place and the carbon passes into the harden- 
ing form. 

Since it is necessary to retain the hardening form of carbon 
and obtain the maximum hardness, together with the finest pos- 
sible structure, it is advisable to heat slightly above the critical 
range and cool quickly. 

Sudden cooling of steel from any temperature below the 
critical range would not produce the maximum hardness. 

Heating to a high temperature and cooling to the critical range 
before quenching results in coarse crystallization and brittleness. 

It is evident then that heating slowly to a temperature just 
above the critical point for the hardening operation will give the 
best possible results. It should therefore be remembered that 
since the position of the critical temperatures varies in the 
different types of steels, the correct hardening temperature like- 
wise varies. 

The increase in hardness of the different grades of steel is 



STEEL AND ITS TREATMENT 39 

governed by quantity of the carbon content, as well as the rate 
of cooling. The rate of cooling in turn is dependent on the size 
of the hardened piece of steel, as well as the nature of the quench- 
ing medium. 

Whatever the quenching medium, whether brine, water or oil, 
its temperature should be kept low enough to prevent adhesion 
of vapor bubbles to the quenched steel. In the selection of oils 
for the operation particular care should be taken to select one of 
uniform quenching speed, one which will not give off large amounts 
of gaseous vapors at comparatively low temperatures, one which 
will not oxidize nor thicken on continued use. 

From the above it is obvious that the hardening of steel con- 
sists in preventing the formation of soft pearlite, but causing the 
formation and retention of the hard constituent called martensite. 

This hardening process, however, has its limitations when 
pieces of large cross sections are treated. It can readily be seen 
that the inside of a comparatively large piece will not cool as 
rapidly on quenching as the outside; hence, the hardening effect 
is diminished and often eliminated. 

Tempering or Drawing 

Hardened steel is generally hardened too hard and oftentimes 
too brittle, so the process of tempering or drawing is resorted to. 

The operation consists of heating the hardened steel to a tem- 
perature between atmospheric and the temperature at which it 
is quenched, whereby a reduction of hardness, tensile strength 
and elastic limit are accompanied by an increase in elongation 
and reduction of area. 

The increase in ductility and softening, however, is proportional 
to the temperature used in the drawing operation. For instance, 
heating hardened steel to a temperature of 212° Fahr., which is 
the temperature at which drawing begins, would have very little 
effect. The changes become more noticeable with increased 



40 STEEL AND ITS TREATMENT 

temperature until the critical temperature is reached when all 
the results obtained by the hardening operation are eliminated 
and the steel is in the same condition it was previous to the 
hardening. 

The time of the drawing operation is largely dependent upon 
the size of the pieces, as well as the temperature. In other words, 
the same results can be obtained by drawing at a slightly lower 
temperature for a longer period of time as at a higher temperature 
for a shorter period of time. 

Ordinarily this operation is carried on in heated oil or molten 
salt or lead-drawing furnaces. However, the old method of open 
furnace drawing for colors is still used for drawing the temper 
in tools extensively. The former tends to give the more accurate 
and uniform results as they afford a means of more uniform 
heating and a better regulation of temperature. The selection 
of temperature and time for each individual type of parts can 
only be worked out by repeated trials until the desired results 
are obtained. 

Carburizing 

Carburizing has risen in the past ten years from a practice of 
which very little was written and very little known to a position 
that has assumed great commercial importance, due primarily to 
the rapid development of the motor car industry. 

It is the demand of this industry to meet the development 
where greatest strength and minimum weight are essential that 
has given the impetus to the marked advance in metallurgy, 
making necessary a corresponding progressiveness in heat treat- 
ing practices in both alloy and straight carbon steels. Present- 
day methods produce results revolutionary in comparison with 
those of only a few years past, and the science is far from being 
a completed one today. 

It is with this knowledge that the following in turn may be 
antedated a few years hence that this work is submitted. Though 



STEEL AND ITS TREATMENT 41 

it contains the most up-to-date practices today it is intended to 
act merely as a guide from which the individual hardener may 
select the information that will be most helpful in each par- 
ticular case which the practical man must select. 

The theory of carburizing depends upon the fact that steel 
and iron have such strong affinity for carbon that when heated 
in a sealed receptacle in contact with carbonaceous material the 
carbon gas is absorbed by the metal. 

The operation of carburization implies that the user in a 
sense makes his own steel, and the details of the operation must 
be thoroughly understood so that it may be conducted with a 
minimum cost and with the maximum certainty and regularity. 

Investigation has proven that the advantages accruing from 
case carburizing represent the most efficient manner of obtaining 
the desired physical properties in most constructions. 

Opinions vary as to the theory of the absorption of carbon 
by the metal. The carbon may combine with the iron at the 
surface to form carbides which diffuse in the metal, or the carbon 
may be diffused in a gaseous condition, the gas giving up its 
carbon to the metal. 

Whatever may be the method, the facts indicate that the best 
results are obtained when carbonaceous vapors or gases are 
present. 

The process of carburizing is one which consists of adding 
such a percentage of carbon to an outside layer of steel as will, 
on correct quenching, produce a hardened surface while the inner 
core of the metal retains its initial character. 

Carburization is governed by, first, the depth of the car- 
burized zone; second, the graduation of the carbon content from 
the outer surface to the core — ^each one well proven by the micro- 
scope and by chemical analysis. 

The percentage of carbon and the depth of penetration are 
dependent upon, first, the composition of the steel subjected 
to carburization; second, the carburizing temperature; third, 



42 STEEL AND ITS TREATMENT 

the length of time the steel is allowed to remain at the car- 
burizing heat; fourth, the nature of the carburizing material 
used. 

Composition of Steels for Carburizing 

It is a well-known fact that low carbon steels are more sus- 
ceptible to carburization than those of high carbon content, 
which explains the decreased rate of penetration during the 
latter part of the carburizing operation. 

Then, again, on using low carbon steels for carburization the 
resultant core remains tough, vsoft and fibrous and enables the 
finished product to resist shock. 

There are elements when alloyed with steel which tend to 
increase the rate of carburization such as chromium and man- 
ganese; while others, such as nickel and silicon, retard carburi- 
zation. 

The initial carbon content of the steel governs the depth of 
case at which maximum brittleness and minimum strength occur, 
so that the higher the original carbon content the lower the ratio 
of depth of case to the diameter of the core. Therefore it is im- 
portant to know that depth of carburizing is partly regulated by 
the carbon content of the original steel. 

Carburizing Temperature 

The carburizing temperature and its uniformity controls the 
degree of carburizing. 

While the theory has been advanced that carburization may 
take place at temperatures below the critical range, experience 
has proven that the low temperatures are very unsatisfactory 
for commercial work. The slight carburized zone obtained at a 
temperature of 705° C. to 788° C. (1300° to 1450° Fahr.) with 
the ordinary graces of carburizing steels is very un-uniform, 
low in carbon content and with little graduation. 









^ 00 



STEEL AND ITS TREATMENT 43 

There are a few special steels, however, principally the chrome 
vanadium steel, which absorb carbon quite readily at low tem- 
peratures. 

The carburizing temperature is dependent upon the carburizing 
material used, inasmuch as some materials will give a 90-point 
case at 871° C. (1600° Fahr.), 105-point case at 899° C. (1650° 
Fahr.), 115-point case at 927° C. (1700° Fahr.), while other 
materials may give a 90-point carbon case at 927° C. (1700° Fahr.). 

It is absolutely necessary to be thoroughly familiar with the 
carburizing material, the results obtained under certain heats, 
length of time required to obtain a certain depth of penetration 
at that temperature, and whether the heats used will affect the 
steel. 

A temperature of 899° C. (1650° Fahr.) is best for most pur- 
poses, taking into consideration the demand for quick carburizing, 
and still retain the physical properties of the steel. 

The carburizing temperature influences the depth of pene- 
tration. The higher the temperature used in carburizing the 
greater the depth of penetration, as shown in Figs. 12, 13, 14. 
Fig, 12 represents a piece of steel carburized for 24 hours at a 
temperature of 874° C. (1605° Fahr.), and shows the least pene- 
tration, whereas the piece carburized for 24 hours at a tem- 
perature of 925° C. (1697° Fahr.), shows a decided deeper pene- 
tration of case (Fig. 13), and Fig. 14, which was carburized at a 
temperature of 1010° C. (1870° Fahr.), gives the deepest case of 
all. 

In hastening the carburizing operation the furnaces may be 
heated to 50° Fahr. above the carburizing temperature until the 
pots are heated throughout and then lowered to the correct car- 
burizing temperature. 

After the carburizing pots have been heated throughout the 
heat must be kept as uniform as possible so as to obtain the best 
results. 

In commercial work, however, there are so many things to be 



44 STEEL AND ITS TREATMENT 

taken into consideration that we think it best to summarize the 
effects of the temperature and thus allow our readers to make 
their selection. 

As a further aid to the hardener, the specifications of the 
American Society of Automobile Engineers are given at the 
close of this treatise. It will be seen that the general character- 
istics are given together with the heats for carburizing and heat 
treatment. These heats are approximate, but in very close range 
for proper refining. 

The Depth of Penetration 

The depth of penetration in a given time, as well as the carbon 
content or percentage of carbon in the carburized zone, are 
governed by the temperature used in carburizing and the 
length of time the work is held at the carburizing heat. 

The higher the temperature used in carburizing the greater 
the depth of penetration and the higher the carbon content of 
the carburized case. All of which has been proven by tests made 
by heating the same work under the same conditions but in- 
creasing the carburizing temperature for each new heat or test. 

The lowest temperature at which uniform penetration can be 
obtained is about 816° C. (1500° Fahr.). 

Work which is not "subjected to shock," but requiring the 
greatest wearing surface, can be carburized at a temperature 
of 927° C. (1700° Fahr.), with a suitable carburizing material to 
obtain a carburized case of Hyper-Eutectoid Composition or 115- 
point carbon, as shown in Fig. 15. 

This micro-photograph shows the black areas as Pearlite and 
the white areas surrounding the Pearlite as excess carbon or 
"Free Cementite." 

Such parts as ball and roller bearings, which require the 
toughest possible case with the greatest hardness, should be 
carburzied at 900° C. (1650° Fahr.), so as to obtain a carburized 




Fig. 15 
Hyper-Eutectoid Case. 115-Point Carbon. White Lines Denote Excess Cementite 



STEEL AND ITS TREATMENT 45 

case of eutectic composition or 90-point carbon as shown in 
Fig. 16; whereas the presence of "Free Cementite" in the car- 
burized case would produce brittleness when subjected to shock 
and heavy load. 

For a given time and temperature the chrome steels seem to 
give the greatest depth of penetration as well as the highest 
carbon content. 

Graduation of case into core increases with the increase of 
temperature in carburizing attaining a maximum at about 912° 
C. (1675° Fahr.). Grain size of the steel increases with in- 
creased temperature. 

Alloy steels, especially chrome vanadium, show the least crys- 
tallization at high temperature. 

Conditions in working, cost of hardening, haste for parts 
needed in production, etc., necessitate that the practical man 
make a close study of his work. The results, while not carrying 
the steel to the highest degrees of hardness but sufficient for the 
present needs, can be obtained by a close study of the effect of 
high carbon case, light or thin penetration, quenching directly 
from the carburizing pot, or allowing the work to cool in the 
pots and reheat to the hardening temperature. 

The above methods are used by many hardeners, knowing 
that they are not obtaining the greatest efficiency in the piece 
treated, but time, conditions in the shop and the cost of pro- 
duction are the excuses for hastening or changing the method 
to obtain the best possible results, such as cooling/in the car- 
burizing pot and heating for core refinement, heating for case 
refinement and drawing, if necessary. 

A carburized case of great depth and high carbon content may 
cause warpage, cracking and brittleness on small parts, while 
a thin, low carbon case is of no value to the work other than 
the benefit the piece receives from the heating and quenching. 
It is important that each hardener make a study of his various 
parts to be hardened. 



46 STEEL AND ITS TREATMENT 

The selection of the best carburizing temperature to obtain 
uniform work of the highest standard requires consideration of 
the composition of the steel to carburize, shape of the boxes, 
fuel, cost of production, etc., all of which we can touch lightly, 
leaving much to the judgment of the individual to regulate con- 
ditions under his control. 

Case-Hardening 

The factors which control case-hardening are: First, carburizing 
materials used; second, style of boxes and method of packing; 
third, the temperature reached; fourth, the length of time held 
at this temperature; fifth, the heat treatment after carburizing; 
sixth, the method of hardening, quenching and tempering; 
seventh, the character of the metal treated. 

A molten bath of potassium cyanide heated to 850° C. (1582° 
Fahr.), and in which the steel articles are immersed, produces 
quick, superficial, hard and even cases. The poisonous character 
of the escaping gases, however, is a serious objection to its use. 

The carburizing of steel may also be performed at the proper 
temperature by means of gases, such as illuminating or other 
gases rich in hydro-carbons. There are a number of commercial 
mixtures offered for sale, all of which possess some or a number 
of good virtues. 

A perfect carburizing material should possess the following 
virtues: 

First — Should carburize quickly, so that the heating will be 
extended over the shortest possible time. 

Second^It must be homogeneous. 

Third — It must carburize at a uniform rate. 

Fourth — It must give a uniform carbon content. 

Fifth — It must not exhaust itself too quickly; that is, it 
must be capable of being used over and over again without 
complete renewal of fresh material. 



^ 



STEEL AND ITS TREATMENT 47 

Carburizing Compound 

A fairly rapid heating carburizing material may in some in- 
stances be desirable; it is by no means essential. The rate of 
penetration of carbon in any grade of steel is normally governed 
by the temperature used in carburizing and the carburizing gases 
liberated by the compound at the carburizing temperature. 

The effect of increasing the temperature is to increase the 
solubility of the carbon in the steel. 

All carburizing mediums do not give the same rate of pene- 
tration at the same temperature. 

Charcoal and coke are not as rapid as leather, bone and other 
compounds rich in hydro-carbons. 

The freedom with which the carburizing gases are liberated 
depends entirely upon the composition of the mixture and the 
form in which the carbonaceous material exists. It is generally 
conceded that carbon monoxide is the true carburizing gas, and 
is developed from solid carburizers by the influence of heat — 
indirectly from the decomposition of hydro-carbon vapor and 
cyanogen and directly from the oxidation of the fixed carbon. 
The hydro-carbons and nitrogen carbons are much more easily 
volatilized by heat than the fixed carbons, which are more graphitic 
in their nature, especially those of mineral origin. 

A compound may thus have a high heat conductivity and yet, 
being composed largely of fixed carbon, will not liberate and form 
the carburizing gases in any quantities until the higher tem- 
peratures are reached. It is not correct, therefore, to assume 
that all carburizers are equally efficient in their rate of pene- 
tration at any one temperature, whether that heat is 816° C. 
(1500° Fahr.) to 927° C. (1700° Fahr.). 

One point necessary in case-hardening is absolute control over 
the carburizing temperatures, especially if the work is to be sub- 
sequently heat treated. Under such conditions the carburizing 
heats must be carried as close to the critical range of the steel 



48 STEEL AND ITS TREATMENT , 

as possible, and yet give a satisfactory case. If this were not 
essential carburizing temperatures could be carried to 1038"^ C. 
(1900° Fahr.), and even above and the time materially shortened. 

The short heats are not the object, as longer and lower ones 
are given to prevent overheating the steel. The effect of high 
temperature on steel is a coarse granular structure which is 
refined only with the greatest difficulty. This is especially true 
on case-hardened work, as it is difficult to refine the core, and 
renders the high carbon case exceedingly weak and brittle with 
a tendency to chip. 

Case-hardening does not improve the quality of the steel 
under the most favorable conditions, and the hardener knows 
it is better to never overheat the metal than try to restore an 
overheated condition. 

To prevent this overheating, therefore, expensive installations 
of pyrometers and thermocouples are used in connection with 
the furnaces, and much care is taken that no variations in the 
carburizing temperatures occur. 

There are carburizing materials on the market whose heats 
cannot be controlled by pyrometers, due to internal combustion 
occurring in the pots which raise the heat of the mixture above 
that indicated by the millivoltmeter. 

The following experiment was conducted to determine internal 
heat of carburizing materials, together with their thermal con- 
ductivity : 

A round box eight inches in diameter filled with the mixture 
was submerged in a molten salt bath to one inch of the top of 
the pot. Two thermocouples were used calibrated with each 
other. One of these was placed in the molten bath and the 
other in the pot through a hole in the center of the lid, which 
was afterwards carefully luted with clay. 

After giving the bath sufficient time to thoroughly heat the 
contents, readings were taken. The temperature of the molten 
salts registered 927° C. (1700° Fahr.), and the temperature of 




Fig. 17 




Fig. 18 
Decarburization 



STEEL AND ITS TREATMENT 49 

the carburizing material in particular was 1008° C. (1846° Fahr.), 
or 146° Fahr. higher than the appHed heat. 

The results of this test indicate plainly that a combustion 
was occurring in the pot which raised the temperature higher 
than that indicated on the instruments. 

Fig. 17 represents a piece of steel carburized with a carburizing 
material of such nature. You will note the coarse crystallization 
of the outer surface of the case which was not refined by a double 
heat treating. This coarse crystallization of the case is a detri- 
ment, as it causes brittleness and chipping of the case. 

The rapidity with which a mixture will transmit heat depends 
largely on its density. Material that is finely powdered will 
not heat as rapidly as material which is coarse. Material that 
is porous will convey heat more rapidly than material that is 
solid. 

However, it does not follow that coarse and porous material 
is more efftcient in its penetrating power on the steel than the 
solid and powdered material. 

The value of a carburizing agent also depends on the kind 
of gases developed by the heat applied. 

Some materials give off oxidizing gases, which oxidize the 
carburized work and result in that condition known as surface 
decarburization. 

We have known of several instances where all the steel car- 
burized in one heat would not harden by quenching even after 
the carburizing operation was repeated, yet the broken part 
showed a good depth of case. Cuts were taken from the outer 
layer and upon analysis showed a surface decarburization to a 
depth of .008 of an inch and a carbon content of .56 per cent. 
The second cut of .01 inch gave a carbon content of .86 per cent. 
Fig. 18 indicates a decarburized condition very plainly. 

Practically speaking, decarburization occurs only with a weak 
carburizer and with low carburizing temperatures. 

Surface decarburization never occurs when a reducing atmos- 



50 STEEL AND ITS TREATMENT 

phere is maintained in the presence of hydro-carbons, due to 
the Uberation of hydrogen gas from their decomposition by heat. 
This point is mentioned as the materials such as bone, etc., 
showing slow heat conduction, are rich in hydro-carbons, while 
in the materials with the greatest thermal conductivity they are 
entirely lacking. 

All carburizing agents have one or more detrimental feature. 
One compound may be dusty, and the fumes poisonous to the 
men doing the packing, while another may exhaust itself quickly 
and therefore be uneconomical. 

In justice to the manufacturers of these materials, it may be 
stated that each mixture is suitable for certain classes of work. 

The compounds unsuitable for a clash gear in an automobile 
transmission may be entirely satisfactory for the carburizing 
of ball and roller bearings. 

Style of Boxes 

After selecting the proper carburizing material the next im- 
portant factor that enters into carburizing is the style of boxes 
or pots for packing the work to be carburized. 

A carburizing pot should be used that withstands the car- 
burizing heat with the least loss in scaling and distortion. 

The design or size of a suitable box for all purposes is 
impossible. The shape of the box should be suited to that of 
the work. 

The walls of the box should not exceed yi inch nor be less than 
yi inch in thickness. Greater thickness would retard heating 
and thinner walls would cause scaling and cracking, thus per- 
mitting access of air. 

To insure more even and rapid heating the boxes should be 
supplied with legs at the bottom corners. 

All unnecessary weight in the boxes should be eliminated so 
as to save time and fuel in raising the temperature of the furnace 
after loading. 



STEEL AND ITS TREATMENT 



51 



The handling of the boxes when hot can be made easier by use 
of a suitable fork, as shown in Fig. 19, or a truck for handUng 
heavier boxes, as shown in Fig. 20. Overhead track with trolley 
and chain hoist can be used in loading and unloading the furnaces. 





Fig. 19 



In motor car work the use of pipes, placed in order in the 
furnaces, filled with cam shafts and other parts of Hke nature 
that require uniform penetration is a common practice. 

Round pots with cored center for gears and small parts are 
used to obtain the most uniform rate of penetration, as shown 
in Figs. 21 and 2 IB. 



52 



STEEL AND ITS TREATMENT 



The study of suitable boxes, pots or pipe for any class of work 
is time well spent. 




Fig. 20 



Packing Pots 

The packing room should, if possible, be separate from the 
room containing the furnaces, so that the packing can be done 
without the discomfort of the heat and dust. Tables on wheels, 
or trucks provided with shelves of the same height as the shelf 
on front of the furnace and large enough to hold the required 




Fig. 21 



STEEL AND ITS TREATMENT 



53 



number of boxes for one furnace, should be provided, so that 
the packed boxes can be easily removed and placed inthe furnace. 

The work to be hardened should be classified according to its 
size and the percentage of carbon required for the particular 
purpose. 

A mixing bin is a great advantage in connection with the 
handhng of case-hardening material. 

When packing a box, first put a layer of the carburizing ma- 
terial on the bottom, the thickness of this layer depending upon 
the size of the pieces to be hardened. If the articles are heavy 




Fig. 2 IB 



they do not require such great care in packing, but with thin 
pieces of peculiar shape greater care is required. 

The pieces should be packed at least one-quarter of an inch 
apart and one-half inch from the sides of the carburizing pot. It 
is advisable to place one inch of carburizing material on top of 
the work under the lid of the pot to prevent the top layer of 
pieces becoming exposed through the shrinkage of the carburizing 
material. 

A lid of the same composition as the carburizing box is placed 
upon the box and the edges luted with a mixture of 50% fire 
clay and 50% sand. 



54 STEEL AND ITS TREATMENT 



Heat Treatment After Carburizing 

For some work after carburizing the box is emptied upon a 
sieve, to separate the work from the compound, and the pieces 
immediately quenched. This practice does not give the maxi- 
mum strength and toughness. 

It is more advisable to allow the work to cool slowly in the 
pot, and when cold it is removed from the box and placed upon 
the floor of the furnace and heated to the hardening temperature 
and quenched. This will give a good case and a tough core, but 
in order to obtain a hard, refined case with a maximum strength 
and toughness, it is heated to a temperature sufficiently high to 
refine the core, and quenched, and then heated again to the 
hardening temperature of the case, and quenched. 

The object of the double quenching operation is to give the 
toughest possible core and the finest crystalline case, and a 
graduation of case, into the core. 

The refining temperatures vary with the composition of the 
steel, and it is advisable to consult the specifications of the 
Society of Automobile Engineers, as given. 

A carbon steel of 10- to 15-point carbon, carburized between 
the temperatures of 843° to 871° C. (1550° to 1600° Fahr.), 
and cooled in the pot and reheated to the hardening tempera- 
ture of the case and quenched will produce a tough core and 
fine, hard, compact case. The temperature in this instance is 
not sufficiently high enough to coarsen the grain of the core. 
When carburizing at 954° C. (1750° Fahr.), the temperature is 
above the critical range and the grain structure is coarsened 
but can be broken up by a double heat treatment to a fairly 
fine grain. 

If strength and resistance to shock are of no importance and 
where surface hardness is the only requirement pieces may be 
quenched directly from the carburizing boxes. The prolonged 



STEEL AND ITS TREATMENT 55 

heating at the high carburizing temperature causes the steel to 
develop an exceedingly coarse grain, which by this method of 
treatment is retained in the finished product. 

Furthermore, during the quenching operation the hot com- 
pound is exposed to the air and considerable is lost by its com- 
bustion. Common practice, where time and cost permit, is to 
allow the work to cool in the boxes before removing and heat 
treating. 

Although where time does not permit the work to cool in 
the pots some concerns are quenching their work directly from 
a carburizing temperature of 871° to 899° C. (1600° to 1650° 
Fahr.), and then reheating to the hardening point of the case 
and quenching. 

Composition of the Metal 

The composition of the metal treated has a marked influence 
on carburizing. 

Some constituents retard the rate of penetration, others in- 
crease it, while some increase brittleness and others reduce it. 

The carbon content of the steel should be below 25 point, as 
the higher the carbon content the greater the brittleness after 
heat treatment. 

Manganese content should be about .35% or less, as 
high manganese renders the carburized case brittle and lowers 
the resistance to shock. Manganese increases the rate of pene- 
tration. 

If, however, steel with higher manganese content is used, 
the detrimental effects can be overcome by alloys, such as 
nickel and chromium. 

Silicon retards the rate of penetration; in fact, steels con- 
taining over 2% of silicon will not absorb carbon. In 
general, it should not exceed .30%. 

Phosphorus and sulphur content should be low. 



56 STEEL AND ITS TREATMENT 

Nickel very materially affects the physical properties, the 
effect being Hmited by the amount of nickel and the carbon 
present. 

Nickel lowers the rate of penetration in proportion to the 
amount present. 

Vanadium lowers the rate of penetration, but as it is used in 
such small quantities, its effects in this respect may be dis- 
regarded. Its influence on the physical properties is pronounced 
and it very materially increases strength, elastic limit and resis- 
tance to shock. 

Chromium increases the rate of penetration of carbon and 
reduces the grain size considerably. 

It slightly increases the difficulties of machining and forging. 

The composition of any steel for carburizing should be regu- 
lated for the purpose intended. 

A fair analysis of a carbon steel for general work is carbon 
10 to 20 point, manganese and siUcon less than .35%, phos- 
phorus and sulphur below .04%. 

The influence of the different elements on the speed of pene- 
tration of carbon when carburizing steels containing the same 
amount of carbon and the different percentages of manganese, 
chromium, nickel and silicon is shown in the following table: 



Speed of 
. Penetration 
per Hour 
Component of Alloys in Inches 

. 5% Manganese 043 

1.0% " 047 

1.0% Chromium 039 

2.0%- " .043 

2.0% Nickel 028 

5.0% " 020 

0.5% Silicon . 024 

1.0% " 020 

2.0% " 016 

5.0% " 000 



STEEL AND ITS TREATMENT 57 



Quenching 



The size of quenching tanks required for any particular class 
of work will depend upon the size of the pieces to be treated. 

It is advisable to have tanks of large capacity for use in 
quenching large pieces of steel. 

After the critical point of the various steels in use has been 
determined, the subject of next importance is the means of 
obtaining the greatest hardness for the particular purpose. 

When a piece of high carbon steel is heated through the 
critical range the carbon passes into the hardening form, and is 
retained in that form by proper cooling or quenching. Therefore, 
it is necessary that we study the speed at which the various 
liquids will cool the piece of steel and the uniformity in rate of 
quenching speed of the quenching mediums. 

Except in special cases high-carbon steels should not be 
quenched in water. Oil should invariably be used. Low-carbon 
steel or steel below 30-point carbon may be quenched in water. 

It is advisable to quench thin pieces in oil regardless of their 
carbon content. 

A piece of steel should be quenched in such a manner as to 
cause the least distortion. Where thick and heavy masses of 
metal are adjacent to thinner and smaller masses the hardener 
will have to use his judgment as to the best method of quenching. 
It is generally customary to quench the piece in such a way that 
the heavier parts come in contact with the quenching medium 
before the thinner parts. 

The selection of the quenching medium is at all times im- 
portant. 

The quenching mediurhs used most extensively are water, 
brine water and oil. 

All hardening baths should be constructed with a view of 
keeping the temperatures of the bath constant at all times. 

This may be obtained by surrounding the tank with water 



58 STEEL AND ITS TREATMENT 

or by means of a circulating system, using pipes running through 
water, or by means of an ice machine. 

Figs. 22, 23, 24, give an illustration of the type of quenching 
baths used most extensively. 

Fresh water in all parts of the country varies slightly from 
hard to soft water, depending upon the location. 

Brine, mixture of water and common salt, is used in circulating 
systems or a small tank. Its use gives greater hardness than 
water and has a tendency to loosen the scale of the pieces when 
quenched and thus lessens the possibilities of soft spots. 

Oil for quenching should be one that possesses the greatest 
quenching speed. The oil should not decompose on continued 
use, nor absorb oxygen from the air and thicken up; it should 
not undergo a fractional distillation, light ends going off and 
heavy ends remaining behind, and should not vary in its quench- 
ing speed. 

Water covered with a few inches of oil is used where the piece 
should be exceedingly hard, but quenching directly in water 
would probably cause hardening cracks. The shock in quench- 
ing is not as severe as in the case of water and the steel obtains 
a hardness almost as great as that obtained from water. A 
quenching medium of this nature is kept cool by means of a 
water jacket. 

In order to successfully harden, one must study the various 
parts, their design and hardness desired. With the above 
quenching mediums a wide range of hardness can be secured 
and any condition satisfied if the bath is modified to suit the 
purpose. 

Carbon Steels 

Specification No. 10-10 
10-Point Carbon Steel 
This is usually known in the trade as soft, basic, open-hearth 
steel. It is a material commonly used for seamless tubing, 



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STEEL AND ITS TREATMENT 



59 



pressed steel frames, pressed steel brakedrums, sheet brakebands 
and pressed steel parts of many varieties. It is soft and ductile 
and will stand much deformation without cracking. 

This steel in a natural or annealed condition is of low strength, 
and must not be used where much strength is required. This 
quality of material is considerably stronger after cold drawing 
or rolling; that is, its yield point is raised by such working. This 
is important in view of the fact that many wire and sheet parts 
above mentioned are used in the cold rolled or cold drawn form. 

It must not be forgotten that when this steel (so cold worked) 
is heated, as for bending, brazing, welding or the like, the yield 
returns to that characteristic of the annealed material. This 
remark also applies to all materials that have an increased yield 
point produced by cold working. 

This material in a natural or annealed state does not machine 
freely. It will tear badly in the turning, threading and broaching 
operations. Heat treatment produces but little benefit, and that 
not in strength but in toughness. It is possible to quench this 
grade of steel and put it in a condition to machine better than 
the annealed state. 

The heat treatment which will produce a little stiffness is to 
quench at 1500° F. in oil or water. No drawing is required. 

This steel will case-harden, but is not as suitable for this 
purpose as Steel 10-20, a note on which follows. 

Physical Characteristics 



Yield point, lbs., per sq. in. 

Reduction of area 

Elongation in 2 in 



Annealed 


Cold Rolled 

or 
Cold Drawn 


28,000 

to 
36,000 

65-55% 
40-30% 


40,000 

to 
60,000 

55-45% 
Unimportant 



60 STEEL AND ITS TREATMENT 

Specification No. 10-20 
20-Point Carbon Steel 

This Steel is known to the trade as 20-point carbon, open- 
hearth steel, and often as machine steel. 

This quality is intended for case-hardening. It forges well 
and machines well, but should be considered as screw machine 
stock. It may therefore be used for a very large variety of forged, 
machined and case-hardened parts of an automobile where 
strength is not paramount. 

Steel of this quality may also be drawn into tubes and rolled 
into cold rolled forms, and, as a matter of fact, makes a better 
frame than Steel 10-10, because of the slightly higher carbon and 
resulting strength. The increased carbon content has no detri- 
mental effect as far as usage is concerned, and it is only the most 
difficult of cold forming operations that cause it to crack during 
the forming. For automobile parts it may be safely used inter- 
changeably with Steel 10-10, as far as cold pressed shapes are 
concerned. 

Heat treatment of this steel produces but Httle change as far 
as strength is concerned, but does cause a desirable refinement 
of grain after forging, and the toughness is materially increased. 
A simple quenching operation from about 816° C. (1500° F.) in 
oil is all that is necessary. Treatment will often help the ma- 
chining qualities. 

Case-hardening is the most important treatment for this 
quality of steel. The character of the operation must depend 
upon the importance of the part to be treated and upon the shape 
and size. There is a certain group of parts in an automobile 
which are not called upon to carry much load or withstand any 
shock. The principal requirement is hardness. Such parts are 
fairly illustrated by screws and by rod-end pins. The simplest 
form of case-hardening will suffice, viz.: 



STEEL AND ITS TREATMENT 61 

Heat Treatment A 
After forging or machining: 

1. Carburize at a temperature between 871° C. and 955° C. 

(1600° F. and 1750° F.), (1650° F. to 1700° F. desired). 

2. Cool slowly or quench. 

3. Reheat to 788° C. to 816° C. (1450° F. to 1500° F.) and 

quench. 

Another class of parts demands the best treatment (Heat 
Treatment B), such as gears, steering-wheel pivot pins, cam- 
rollers, push-rods and many similar details of an automobile 
which the manufacturer learns by experience must be not only 
hard on the exterior surface but must possess strength as well. 
The desired treatment is one which first refines and strengthens 
the interior and uncarburized metal. This is then followed by 
a treatment which refines the exterior, carburized, or high-carbon 
metal. 

Heat Treatment B 

After forging or machining: 

1. Carburize at a temperature between 871° C. and 955° C. 

(1600° F. and 1750° F.), (1650° F. to 1700° F. desired). 

2. Cool slowly in the carburizing mixture. 

3. Reheat to 816° C to 844° C. (1500° F. to 1550° F.). 

4. Quench. 

5. Reheat to 760° C. to 788° C. (1400° F. to 1450° F.). 

6. Quench. 

7. Draw in hot oil at a temperature which may vary from 

149° C. to 231° C. (300° F. to 450° F.), depending upon 
the degree of hardness desired. 

In the case of very important parts, the last drawing opera- 
tion should be continued from one to three hours, to insure the 
full benefit of the operation. 



62 



STEEL AND ITS TREATMENT 



The objects of drawing are two-fold; first, and not least im- 
portant, is the reHeving of all internal strains produced by 
quenching; second is the decrease in hardness, which is some- 
times desirable. The hardness begins to decrease very materially 
from 350° F. up, and the operation must be controlled as dictated 
by experience with any given part. 

There are certain very important pieces that demand all of 
these operations, but the last drawing operation may be omitted 
with a large number. Experience teaches what degree of hard- 
ness and toughness combined is necessary for any given part. 
It is impossible to lay down a general rule covering all different 
uses. If the fundamental principle is well understood, there 
should be no trouble in developing the treatment to a proper 
degree. 

Following the foregoing treatment, a fractured part should 
show a fine grained exterior, without any appearance of shiny 
crystals. The smaller the crystals the better. The interior may 
show a silky, fibrous condition or a fine crystalline condition; 
but it must not show a coarse, shiny, crystalline condition. 

Physical Characteristics 



Yield point, lbs., per sq. in. 

Reduction of area 

Elongation in 2 in 



Annealed 



30,000 

to 
40,000 
60-45% 

35-25% 



Cold Rolled 

or 
Cold Drawn 



40,000 

to 
75,000 

35-30%o 
Unimportant 



Heat Treat- 
ment C or D 



40,000 

to 

75,000 

60-30%o 

35-15% 



There is little use in giving the physical characteristics of a 
carburized steel, inasmuch as any test must be deceptive be- 
cause of the very high carbon exterior case which cracks and 
fails long before the soft and tough interior does. This means 
that the rupture is fragmental and progressive and misleading. 



STEEL AND ITS TREATMENT 63 

Specification No. 10-30 
30-Point Carbon Steel 

This material is sometimes referred to in the trade as 30-point 
carbon machine steel. 

It is primarily for use as a structural steel. It forges well, 
machines well and responds to heat treatment in the matter of 
strength as well as toughness; that is to say, intelligent heat 
treatment will produce marked increase in the yield point. It 
may be used for all forgings, such as axles, driving shafts, steering 
pivots and other structural parts. It is the best all-round struc- 
tural steel for such use as its strength warrants. 

Heat treatment for toughening and strength is of importance 
with this steel. The heat treatment must be modified in accord- 
ance with the experience of the individual user, to suit the size 
of the part treated and the combination of the strength and 
toughness desired. The steel should be heat treated in all cases 
where reliability is important. 

Machining may precede the following heat treatment, depend- 
ing somewhat upon the convenience and the character of the 
treatment. If the highest strength is demanded, a strong quench- 
ing medium must be employed; for example, brine. In such 
case, the yield point will be correspondingly high and the steel 
correspondingly hard and difficult to machine. On the other hand, 
if a moderately high yield point is all that is desired, an oil quench 
will suffice and machining may follow without any difficulty 
whatever. 

Heat Treatment C 

After forging or machining: 

1. Heat to 802° C. to 829° C. (1475° F. to 1525° F.). 

2. Quench. 

3. Reheat to 316° C. to 649° C. (600° F. to 1200° F.) and 

cool slowly. 



64 STEEL AND ITS TREATMENT 

This is the simplest form of heat treatment. The drav/ing 
operation (No. 3) must be varied to suit each individual case. 
If great toughness and little increased strength are desired, the 
higher drawing temperatures may be used; that is, in the neigh- 
borhood of 593° C. to 649° C. (1100° F. to 1200° F.). If much 
strength is desired and little toughness, the lower temperatures 
are available. Even the lowest of the temperatures given will 
produce a quality of steel, after oil quenching, that is very tough 
— sufficiently tough for many important parts. In fact, with 
some parts the drawing operation (No. 3) maybe entirely omitted. 

Results better than obtainable with the above sequence of 
operations may be obtained by a double treatment, viz.: 

Heat Treatment D 
After forging or machining: 

1. Heat to 816° C. to 844° G. (1500° F. to 1550° F.). 

2. Quench. 

3. Reheat to 760° C. to 788° C. (1400° F. to 1450° F.). 

4. Quench. 

5. Reheat to 316° C. to 649° C. (600° F. to 1200° F.) and 

cool slowly. 

This produces a refinement of grain not possible with one 
treatment and is resorted to in parts where extremely good 
qualities are desired. 

This quality of steel is not intended for case-hardening, but 
by careful treatment it may be safely case-hardened. This 
should be in emergencies only, rather than as a regular practice 
and, if at all, only with the double treatment followed by the 
drawing operation; that is, the most painstaking form of case- 
hardening. 



STEEL AND ITS TREATMENT 
Physical Characteristics 



65 



Yield point, lbs., per sq. in. 

Reduction of area 

Elongation in 2 in 



Annealed 



35,000 

to 
45,000 

55-40% 
30-20% 



Cold Rolled 

or 
Cold Drawn 



Not usually 
worked in 

this manner, 

except for 

wire 



Heat 

Treatment 

C or D 



40,000 
to 

80,000 
60-30%, 
30-10% 



Specification No. 10-40 
40-Point Carbon Steel 

This material is ordinarily known to the trade as 40-point 
carbon machine steel. 

This quality represents a structural steel of greater strength 
than Steel 10-30. Its uses are more limited and are confined in 
a general way to such parts as demand a high degree of strength 
and a considerable degree of toughness. At the same time, with 
proper heat treatment the fatigue-resisting (endurance) qualities 
are very high — higher than with any of the foregoing specifica- 
tions. . 

This steel is commonly used for crank shafts, driving shafts 
and propeller shafts. It has also been used for transmission 
gears, but it is not quite hard enough without case-hardening 
and is not tough enough with case-hardening to make safe trans- 
mission gears. It should not be used for case-hardened parts, 
except in an emergency. Other specifications are decidedly 
better for this purpose. 

In a properly annealed condition it machines well — -not well 
enough for screw machine work, but certainly well enough for 
all-around machine shop practice. 

A good heat treatment for this quality of steel for crank 
shafts and similar parts is as follows: 



66 



STEEL AND ITS TREATMENT 



Heat Treatment E 
After forging or machining: 

1. Heat to 816° C. to 844° C. (1500° F. to 1550° F.). 

2. Cool slowly. 

3. Reheat to 760° C. to 788° C. (1400° F. to 1450° F.). 

4. Quench. 

5. Reheat to 316° C. to 649° C. (600° F. to 1200° F.) and cool 

slowly. 

Physical Characteristics 



Yield point, lbs/, per sq. in. 

Reduction of area 

Elongation in 2 in 



Annealed 



40,000 

to 
50,000 

50-40% 

25-20% 



Heat Treat- 
ment E 



45,000 

to 
100,000 

55-25% 
25- 5% 



Specification No. 10-50 
50-Point Carbon Steel 

This Specification differs very little from Steel 10-40. Owing 
to its higher carbon content it is somewhat harder to machine, 
but not seriously. It is also somewhat stronger. It can be used 
for gears with a little better result than the preceding specifi- 
cation. The same form of heat treatment may be used, with 
suitable modifications to fit individual cases. 



Physical Characteristics 



Yield point, lbs., per sq. In. 

Reduction of area 

Elongation in 2 in 



Annealed 



45,000 
to 

60,000 
40-30% 
20-15% 



Heat Treat- 
ment E 



50,000 

to 
110,000 

50-15% 
20- 5% 



STEEL AND ITS TREATMENT 67 

Specification No. 10-80 

80-Point Carbon Steel 

This quality is ordinarily known to the trade as spring steel. 
Its use generally is for springs of light section. 

The hardening and drawing of springs; that is, the heat 
treatment of them, is, as a rule, in the hands of the spring-maker, 
but in case it is desired to treat, as for small springs, the follow- 
ing is recommended. 

Heat Treatment F 

After shaping or coiling: 

1. Heat to 788° C. to 816° C. (1450° F. to 1500° F.). 

2. Quench in oil. 

3. Reheat to 204° C. to 427° C. (400° F. to 800° F.), in accord- 
ance with degree of temper desired, and cool slowly. 

It must be understood that the higher the drawing tempera- 
ture (Operation 3), the lower will be the yield point of the ma- 
terial. On the other hand, if the material be drawn at too low a 
temperature, it will be brittle. A few practical trials will locate 
the best temper for any given shape or size. 

Physical Characteristics 

The physical characteristics of heat treated spring steel are 
best determined by transverse test. This is because steel as 
hard as tempered spring steel is very difficult to hold firmly in 
the jaws of a tensile testing machine. There is more or less slip, 
and side strains are bound to occur, all of which tend to produce 
misleading results. 

The physical characteristics in the annealed condition may 
be omitted, inasmuch as this grade of steel is not ordinarily used 
for structural parts in such condition. 

Careful examination of the fracture of the treated material is 
desirable. After tempering no suitable spring steel should be 
coarsely crystalline. It should be finely crystalline, and in some 
cases show a partly fibrous fracture. 



68 



STEEL AND ITS TREATMENT 

Physical Characteristics 

(Transverse Test) 





Heat Treatment F 


Elastic limit (initial set), lbs. 
Reduction of area 


per sq. in 

. 


90,000 to 160,000 
Not determined in trans- 


Elongation 


verse test 
Not determined in trans- 
verse test 



Specification No. 10-95 

95-Point Carbon Steel 

This is a grade of steel used generally for springs. Properly 
heat treated, extremely good results are possible. Substantially 
the same remarks apply to this quality of steel as to Steel 10-80. 
It is possible that the quenching temperature (Operation 1, Heat 
Treatment F) may be lowered slightly because of the increase 
in carbon, and it is also probable that the drawing temperature 
(Operation 3) will not be the same. 

Physical Characteristics 

The physical characteristics of a tempered spring of this qual- 
ity are substantially those of Steel 10-80, possibly a little higher. 
The thought will naturally arise as to what is to be gained by 
the use of this material. The answer is that this steel will possess 
a finer grain and endure longer, providing the treatment is suit- 
able; also, that with thicker and heavier metal the treatment will 
penetrate deeper because of the increased carbon content. It is 
for this reason that this quality of steel should be used for the 
heavier types of springs. 

The same remarks as made in regard to tests and inspection 
in connection with Steel 10-80 apply to this steel. 



STEEL AND ITS TREATMENT 



69 



Special Alloys 
Nickel 

The hardening and annealing of nickel steels should be con- 
ducted at lower temperatures than the hardening and annealing 
of ordinary steels of similar carbon content, since their critical 
points occur at a lower temperature. Investigations seem to 
indicate that between and 5% nickel containing low 
percentages of carbon, each 1% of nickel lowers the Ar^ point 
some 20 degrees C, and the Ac^ point about 10 degrees. In 
the low nickel steels of commerce the points Ar^ and Ac^ 
should occur at or near the temperatures indicated in the follow- 
ing table, according to their precentages of nickel: 



Per Cent. Nickel 


Aci 


Ari 





750°C. 


700°C. 


0.50 


745 


690 


1.00 


740 


680 


1.50 


735 


670 


2.00 


730 


660 


2.50 


725 


650 


3.00 


720 


640 


3.50 


715 


630 


4.00 


710 


620 


4.50 


705 


610 


5.00 


700 


600 



Nickel was added to carbon steel as the result of investigations 
which were started for the purpose of overcoming the "sudden 
rupture" that is inherent in carbon steel products. Nickel steel 
is used to a large extent in the construction of high-grade ma- 
chinery and can be purchased in the open market today in almost 
any percentages of nickel from up to 36%, and with the 
carbon component varying between 0.10 and 1.00%. Thus 
it covers a wide field or usefulness in which greater strength 



70 



STEEL AND ITS TREATMENT 



and wearing qualities and other properties are demanded than 
can be obtained in the ordinary steel. 

The most widely used nickel steel is that containing 3.5% 
nickel, with a carbon content ranging from .15 to .25% for 
case carburizing purposes and .30 to .40% for parts subjected 
to vibration, shock or torsional stresses. 

Their physical characteristics are as follows: 



.30% TO .40% Carbon, 3.5% Nickel 




Oil Treated 850° and 
Drawn 550° C. 



Elastic limit 

Ultimate strength . 
Elongation in 2 in. 
Reduction of area . 



90,000 lbs. per sq. in. 
127,000 " " " " 

21% 
57% 



.15% to .25% Carbon, 3.5% Nickel 




Core of Case-Hardened 
Specimen 



Elastic limit 

Ultimate strength . 
Elongation in 2 in. 
Reduction of area . 



95,000 lbs. per sq. in. 
110,000 " " " " 

18% 
60% 



Nickel gives to steel one peculiar property, in that it can be 
added in percentages up to 8, and the tensile strength and 
elastic limit will be raised by so doing. But in percentages 
from 8 to 15 a zone of brittleness is produced, while at 16% 
the strength and toughness are returned, and from there on 
the strength and toughness gradually decrease while the elonga- 
tion increases. 



STEEL AND ITS TREATMENT 



71 





Analysis 


Unannealed Test 
Bar 


Annealed Test Bar 








Elastic 


Ultimate 


Elon. 
in 2 

in r' 


Re- 


Elastic 


Ultimate 




Red. 








Limit, 


vStrength, 


duc. 


Limit, 


Strength, 


Elon. 


of 


c. 


Mn. 


Ni. 


lbs. per 


lbs. per 


of 


lbs. per 


lbs. per 


in 2 


Area 








sq. in. 


sq. in. 


in., ^( 


Area 


sq. in. 


sq. in. 


in.,'fc 


i 


0.19 


0.79 


0.27 


42,560 


69,440 


35 


56 


44,800 


62,720 


31 


52 


0.14 


0.75 


0.51 


44,800 


67,200 


36 


62 


47,040 


60,540 


41 


63 


0.13 


0.72 


0.95 


56,000 


73,920 


31 


53 


44,800 


60,540 


41 


63 


0.14 


0.72 


1.92 


58,240 


76,160 


33 


55 


49,280 


69,440 


36 


53 


0.19 


0.65 


3.82 


62,720 


82,880 


30 


54 


56,000 


73,920 


35 


55 


0.18 


0.65 


5.81 


62,720 


91,840 


27 


40 


62,720 


82,880 


33 


51 


0.17 


0.68 


7.65 


69,440 


109,760 


26 


42 


67,200 


100,800 


26 


41 


0.16 


0.86 


9.51 


94,080 


190,400 


9 


18 


71,680 


125,440 


2 


2 


0.18 


0.93 


11.39 


145,600 


210,560 


12 


24 


100,800 


199,360 


12 


26 


0.23 


0.93 


15.48 


123,200 


210,560 


3 


2 




152,320 


1 


1 


0.19 


0.93 


19.64 


105,280 


203,840 


7 


6 


l66,800 


194,880 


5 


4 


0.16 


1.00 


24.51 


71,680 


172,480 


13 


14 


56,000 


174,720 


14 


8 


0.14 


0.86 


29.07 


56,000 


85,120 


33 


44 


35,840 


82,880 


48 


51 


0.16 


1.08 


49.65 


(No test made) 






33,600 


80,640 


49 


53 



While nickel retards the carburization of steel by case-harden- 
ing, the cores of nickel steel articles are not coarsened by the 
high temperature of the carburizing operation to the same extent 
as straight carbon steel cores. This, together with the fact that 
it readily produces a martensitic structure, which is desirable 
in case-hardened parts, upon increasing the carbon content 
makes it extremely useful for case carburized articles, such as 
gears, pinions, etc. 



Chromium 

Chromium is said to have little, if any, direct influence on the 
position of the critical points. Chrome steels that are utilized 
for constructive material seldom contain more than 3% chro- 
mium. The presence of chromium increases the hardness and 
the hardening power of the metal. Chromium has the effect 
of increasing the elastic limit of steel, especially when it is com- 
bined with nickel or vanadium. 



72 



STEEL AND ITS TREATMENT 



The presence of both nickel and chromium In steel produces a 
metal possessing the valuable qualities of both nickel and chro- 
mium steels, namely high elastic limit, combined with high duc- 
tility, greater hardness, hardening power, and better wearing 
qualities than carbon steel. They are used extensively in 
automobile construction, as well as in all parts that are sub- 
jected to high stresses. 



Vanadium 

Vanadium has no marked influence on the position of the 
critical points. 

It appears to act directly in several different ways— in low 
and medium carbon steels it toughens the metal, mainly by its 
solid solution in the carbonless portion, or Ferrite. It also forms 
complex carbides which, especially with chromium or nickel, or 
with both, greatly strengthen the steel. A very small amount 
of vanadium will largely enable the steel to resist deteriora- 
tion, which under continued vibration leads to brittleness. The 
following tables show some of the types and physical properties 
of the chrome vanadium steels most commonly used: 

Type "A" 



Carbon ... 
Manganese. 
Chromium. 
Vanadium . 



Mild 



0.18 to 0.25% 

0.35 to 0.50%o 

0.60 to 0.80%o 

over 0.16%o 



Regular 



0.25 to 0.32% 

0.40 to 0.60% 

0.80 to 1.00%o 

over 0.16%o 



Full 



0.32 to 0.40% 

0.40 to 0.60%, 

0.80 to 1.00% 

over 0.16%o 



Type "D' 





Mild 


Regular 


Full 


Carbon 

Manganese 

Chromium 

Vanadium 


0.35 to 0.43%o 

0.70 to 0.90% 

0.80 to 1.10%o 

over 0.16% 


0.43 to 0.52% 

0.70 to 0.90%o 

0.80 to 1.10%o 

over 0.16% 


0.52 to 0.60% 

0.60 to 0.80% 

0.80 to 1.10% 

over 0.16S'7o 



STEEL AND ITS TREATMENT 



73 



Type "A" Mild 
(Quenched in water at 917° C. (1683° F.) and drawn as follows) 



Drawing Temperature 


Carbon 


Elastic 
Limit 


Ultimate 
Strength 


Elongation 
in 2 in. 


Reduction 
of Area 


350° C. (662° F.) 


.28 


110,600 


134,520 


14.8% 


47.3% 


400° C. (752° F.) 


.27 


128,190 


143,460 


15.3% 


48.0% 


450° C. (842° F.) 


.28 


124,030 


144,200 


14.7% 


51.7% 


500° C. (932° F.) 


.25 


106,200 


124,490 


18.4% 


60.6% 


550° C. (1022° F.) 


.25 


106,330 


124,140 


18.8% 


59.5% 


600° C. (1112° F.) 


.25 


113,100 


131,710 


18.4% ■ 


56.8% 


650° C. (1202° F.) 


.24 


105,260 


123,340 


20.0% 


60.7% 


700° C. (1292° F.) 


.25 


103,180 


117,640 


21.0% 


64.5% 


750° C. (1382° F.) 


.26 


87,410 


101,570 


23.5% 


67.0% 


800° C. (1472° F.) 


.26 


65,710 


83,870 


29.6%o 


70.4% 



Type "A" Regular 
(Quenched in water from 917° C. (1683° F.) and drawn as indicated) 



350° C. (662° F.) 


.33 


143,440 


153,550 


14.4% 


52.9% 


400° C. (752° F.) 


.30 


147,390 


158,380 


14.0% 


50.9% 


450° C. (842° F.) 


.30 


138,690 


155,030 


15.0% 


54.9% 


500° C. (932° F.) 


.28 


125,500 


143,580 


16.3% 


58.2% 


550° C. (1022° F.) 


.33 


122,370 


139,230 


16.6% 


57.1% 


600° C. (1112° F.) 


.30 


126,020 


140,280 


18.3% 


59.5% 


650° C. (1202° F.) 


.27 


124,180 


140,250 


19.3% 


62.8% 


700° C. (1292° F.) 


.27 


116,310 


127,720 


23.3% 


66.3% 


750° C. (1382° F.) 


.28 


93,280 


107,910 


23.6% 


69.8% 


800° C. (1472° F.) 


.28 


76,670 


95,060 


28.2% 


71.0% 



Type "A" Full 
(Quenched in water from 917° C. (1683° F.) and drawn as indicated) 



350° C. (662° F.) 


.39 


158,550 


171,700 


11.1% 


41.6% 


400° C. (752° F.) 


.38 


168,400 


180,180 


11.3% 


40.0%o 


450° C. (842° F.) 


.39 


158,210 


171,000 


11.5% 


43.6% 


500° C. (932° F.) 


.39 


146,980 


164,900 


13.8% 


52.3% 


550° C. (1022° F.) 


.38 


136,300 


152,050 


16.0% 


54.5% 


600° C. (1112° F.) 


.38 


132,950 


151,700 


15.7% 


56.3% 


650° C. (1202° F.) 


.36 


119,940 


142,200 


17.7% 


58.9% 


700° C. (1292° F.) 


.35 


117,660 


130,520 


19.5% 


65.2% 


750° C. (1382° F.) 


.35 


96,520 


111,630 


23.5% 


69.2% 


800° C. (1472° F.) 


.34 


74,110 


93,420 


29.7% 


69.0% 



74 



STEEL ANU ITS TREATMENT 



Type "D" Mild 
(Quenched in water from 917° C. (1683° F.) and drawn as indicated) 



Drawing Temperature 


Carbon 


Elastic 
Limit , 


Ultimate 
Strength 


Elongation 
in 2 in. 


Reduction 
of Area 


350° C. (662° F.) 


.47 


220,350 


235,570 


10.8% 


39.2% 


400° C. (752° F.) 


.48 


217,330 


228,570 


10.1% 


38.9% 


450° C. (842° F.) 


.44 


201,230 


208,300 


10.6% 


40.9% 


500° C. (932° F.) 


.46 


185,660 


195,010 


11.8% 


43.4% 


550° C. (1022° F.) 


.45 


171,720 


180,040 


13.3% 


48.8% 


600° C. (1112° F.) 


.42 


163,600 


172,750 


14.4% 


49.2% 


650° C. (1202° F.) 


.44 


152,450 


161,470 


17.0% 


55.9% 


700° C. (1292° F.) 


.44 


125,360 


134,330 


20.5% 


64.2% 


750° C. (1382° F.) 


.44 


103,470 


116,290 


24.1% 


66.8% 


800° C. (1472° F.) 


.42 


77,420 


99,840 


28.3% 


68.5% 



Type "D" Regular 
(Oil treated from 911° C. (1672° F.) and drawn as indicated) 



350° C. 
400° C. 
450° C. 
500° C. 
550° C. 
600° C. 
650° C. 
700° C. 
750° C. 
800° C. 



(662° F.) 


.46 


(752° F.) 


.44 


(842° F.) 


.45 


(932° F.) 


.45 


(1022° F.) 


.47 


(1112° F.) 


.45 


(1202° F.) 


.46 


(1292° F.) 


.47 


(1382° F.) 


.46 


(1472° F.) 


.44 



213,760 
182,410 
182,760 
175,440 
165,060 
149,690 
142,360 
122,340 
100,950 
78,570 



226,580 
193,120 
193,380 
179,780 
177,640 
165,140 
157,190 
135,930 
115,300 
100,820 



7.5% 
11.3% 
11.2% 
11.9% 
12.9% 
14.6% 
16.0% 
19.0% 
23.2% 
28.0% 



26.9% 
44.0% 
42.6% 

43.5% 
45.7% 
50.5% 
54.5% 
60.4% 
64.8% 
67.0% 



Type "D" Full 
(Oil treated from 911° C. (1672° F.) and drawn as indicated) 



350° C. (662° F.) 


.65 


272,160 


280,580 








400° C. (752° F.) 


.65 


257,610 


265,580 


4.2% 


9.8% 


450° C. (842° F.) 


.66 


244,340 


251,900 


7.0% 


25.3% 


500° C. (932° F.) 


.65 


223,200 


232,290 


9.4% 


31.8% 


550° C. (1022° F.) 


.65 


206,860 


215,160 


9.8% 


30.8% 


600° C. (1112° F.) 


.67 


195,250 


204,610 


11.1% 


32.7% 


650° C. (1202° F.) 


.65 


175,640 


183,780 


13.3% 


41.0% 


700° C. (1292° F.) 


.62 


139,340 


148,920 


18.0% 


52.2% 


750° C. (1382° F.) 


.62 


115,190 


126,810 


22.6% 


58.7% 


800° C. (1472° F.) 


.62 


85,640 


113,610 


25.7% 


64.4% 



STEEL AND ITS TREATMENT 75 

Nickel Steels 

Specification No. 23-15 
15-Point Carbon, 3}4% Nickel Steel 

This quality of steel is embraced in these specifications to 
furnish a nickel steel that is suitable for carburizing purposes. 
Steel of this character, properly carburized and heat treated, 
will produce a part with an exceedingly tough and strong core, 
coupled with the desired high carbon exterior. 

This steel is also available for structural purposes, but is not 
one to be selected for such purpose when ordering materials. 
Much better results will be obtained with one of the other nickel 
steels of higher carbon. 

It is intended for case-hardened gears, for both the bevel 
driving and transmission systems, and for such other case- 
hardened parts as demand a very tough, strong steel with a 
hardened exterior. 

The case-hardening sequence may be varied considerably, as 
with Steel 10-20, those parts of relatively small importance re- 
quiring a simpler form of treatment. As a rule, however, those 
parts which require the use of nickel steel require the best type 
of case-hardening, viz.: 

Heat Treatment G 
After forging or machining: 

1. Carburize at a temperature between 871° C. and 955° C. 

(1600° F. and 1750° F.), (1650° F. to 1700° F. desired). 

2. Cool slowly in the carburizing material. 

3. Reheat to 816° C. to 844° C. (1500° F. to 1550° F.). 

4. Quench. 

5. Reheat to 705° C. to 766° C. (1300° F. to 1400° F.). 

6. Quench. 



76 



STEEL AND ITS TREATMENT 



7. Reheat to a temperature from 12r C. to 260° C. (250° F. 
to 500° F.) — in accordance with the necessities of the 
case — and cool slowly. 

The second quench (Operation 6) must be conducted at the 
lowest possible temperature at which the material will harden. 
It will be found that sometimes this is lower than 1300° F. 

In connection with certain uses it will be found possible to 
omit the final drawing (Operation 7) entirely, but for parts of 
the highest importance this operation should be followed as a 
safeguard. Parts of intricate shape, with sudden changes of 
thickness, sharp corners and the like, particularly sliding gears, 
should always be drawn, in order to relieve the internal strains. 

Much is to be learned from the character of the fracture. 
The center should be fibrous in appearance, and the exterior 
high carbon metal, closely crystalline or even silky. 

When used for structural purposes, the physical characteristics 
will range about as follows: 

Physical Characteristics 



Annealed 



Heat Treat- 
ment H or K 



Yield point, lbs, per sq. in. 

Reduction of area 

Elongation in 2 in 



35,000 

to 
45,000 
65-45% 



40,000 
to 

80,000 
65-40% 
35-15% 



Specification No. 23-20 j 

20-Point Carbon, 3>^% Nickel Steel \ 

This quality may be used interchangeably with Steel 23-15. i 
Although intended primarily for case-hardening, it may be prop- ! 



STEEL AND ITS TREATMENT 



77 



erly used for structural parts, with suitable heat treatment, and 
will give elastic limits somewhat higher than material provided 
by the preceding specifications. 

For case-hardening, Heat Treatment G should be followed, 
and for structural purposes the treatment should be in accordance 
with Heat- Treatment H or K, the quenching temperatures, as 
with other steels, being modified to meet individual cases. 



Physical Characteristics 



Annealed 



Heat Treat- 
ment H. or K 



Yield point, lbs. per sq. in. 

Reduction of area 

Elongation in 2 in 



40,000 
to 

50,000 
65-40% 
30-20% 



50,000 

to 
125,000 
65-40% 
25-10% 



Specification No. 23-25 
25-Point Carbon, 3>^% Nickel Steel 

This is a quality of steel that may be case-hardened success- 
fully. Suitable treatment (G) gives a product that is satisfactory 
for gears, whether of the transmission or rear axle bevel type. 
The treatment after carburizing must be slightly modified to 
meet the increase in carbon content. 

This is also a useful quality of steel for many structural parts, 
its response to heat treatment (either H or K) being most satis- 
factory. 

The physical characteristics of this steel may be considered 
as practically those obtained with Steel 23-20, slight modifica- 
tions in the treatment much more than offsetting the slight 
difference in the carbon content. 



78 



STEEL AND ITS TREATMENT 
Physical Characteristics 



Annealed 



Heat Treat- 
ment H or K 



Yield point or elastic limit, lbs. per sq. in. 

Reduction of area 

Elongation in 2 in 



40,000 
to 

50,000 
60-40% 
30-20% 



60,000 

to 
130,000 
60-30% 

25-10% 



Specification No. 23-30 
30-Point Carbon, 3>^% Nickel Steel 

This quality of steel is primarily for heat treated structural 
parts where strength and toughness are sought; such parts as 
axles, front-wheel spindles, crank shafts, driving "shafts and 
transmission shafts. 

Wide variations of yield point or elastic limit are possible by 
the use of different quenching mediums — oil, water or brine — 
and variation in drawing temperatures, from 500° F. up to 1200°F. 

The form of treatment is: 

Heat Treatment H 

After forging or machining: 

1. Heat to 816° C. to 844° C. (1500° F. to 1550° F.). 

2. Quench. 

3. Reheat to 316° C. to 649° C. (600° F. to 1200° F.) and cool 

slowly. 
A higher refinement of this treatment is: 

Heat Treatment K 
After forging or machining: 

1. Heat to 816° C. to 844° C. (1500° F. to 1550° F.). 

2. Quench. 

3. Reheat to 705° C. to 760° C. (1300° F. to 1400° F.). 

4. Quench. 



STEEL AND ITS TREATMENT 



79 



5. Reheat to 316° C. to 649° C. (600° F. to 1200° F.), and cool 
slowly. 

This material may be case-hardened, but is rather high carbon 
for the practice of the average case-hardening department. The 
lower ranges of carbon — in the neighborhood of ,25 — are satis- 
factory, but the upper ranges — in the neighborhood of .35 — 
approach the danger point, and steel of the latter carbon content 
must be correspondingly carefully handled. 

Physical Characteristics 



Annealed 



Heat Treat- 
ment H or K 



Yield point or elastic limit, lbs. per sq. in. 

Reduction of area 

Elongation in 2 in 



45,000 

to 
55,000" 

55-35% 
25-15% 



65,000 

to 
150,000 

55-25% 
25-10% 



Specification No. 23-35 

3 5 -Point Carbon, 3>^% Nickel Steel 

This quality of steel is subject to precisely the same remarks 
as Steel -23-30. It will respond a little more sharply to heat 
treatment and can be forced to higher elastic limits. The differ- 
ence will be small except in extreme cases. 

Physical Characteristics 



Yield point or elastic limit, lbs. per sq. in. 

Reduction of area 

Elongation in 2 in 



Annealed 



45,000 

to 
55,000 

55-35% 
25-15% 



Heat Treat- 
ment H or K 



65,000 

to 
160,000 

55-25% 
25-10% 



80 



STEEL AND ITS TREATMENT 



Specifications Nos. 23-40, 23-45 and 23-50 
40-Point Carbon, 3>^% Nickel Steel 
45-Point Carbon, 3>^% Nickel Steel 
50-Point Carbon, ^}4% Nickel Steel 

The above nickel steels are qualities not in wide use but avail- 
able . for certain purposes. 

The carbon contents being higher than generally used, greater 
hardness is obtainable by quenching; and as increased brittle- 
ness accompanies the greater hardness, the treatments given must 
be modified to meet such condition. For example, the final 
quench may be at a considerably lower temperature, and the 
final drawing temperature, or partial annealing, must be care- 
fully chosen in order to produce the desired toughness and 
other physical characteristics. 

The strength of these steels, as with Steels 23-25, 23-30 and 
23-35, depends' upon the treatment and may be controlled closely 
over a wide range. The degree of brittleness must be carefully 
watched and controlled. Proper treatment will yield very strong 
and tough steel; not as tough as Steel 23-25, 23-30 and 23-35, 
but nevertheless tough enough to fill a number of needs. 



Physical Characteristics 






Annealed 


Heat Treat- 
ment H or K 


Yield point or elastic limit, lbs. per sq. in. . . . 

Reduction of area ' 

Elongation in 2 in 


55,000 

to 
70,000 

50-30% 
25-15% 


70,000 

to 
200,000 

55-15% 
20- 5% 



Nickel Chromium Steels 

These classes of alloy steel are important. There are three 
types in common use, the differences between them consisting 
in the amount of alloying elements present. The types may be 



STEEL AND ITS TREATMENT 81 

classified as low-nickel, medium- nickel and high-nickel chromium 
steels, viz., classes 31, 32 and 33, as given in the specifications. 
In general it may be said that the heat treatments and the 
properties induced thereby are much the same as in. the case of 
plain nickel steels, except that the effects of the heat treatments 
are somewhat augmented by the presence of the chromium, and 
further that these effects increase in these three types with 
increasing amounts of nickel and chromium. 

Specifications Nos. 31-15 to 31-50 

Low-Nickel Chromium Steels 

Substantially the same remarks apply to these various types 
as apply to nickel steels. In other words, the carbon content 
may be varied from the lowest to the highest, depending upon 
the physical qualities sought. The physical characteristics ob- 
tainable will vary with the carbon, and the heat treatment must 
be chosen accordingly. 

Steels 31-15 and 31-20 (15-point and 20-point carbon) are 
intended primarily for case-hardening (Heat Treatment G). 
These steels ought not to be used in the natural condition, but 
if desired may be used for structural purposes, in which case 
Heat Treatment H or K is recommended. 

Steels 31-25, 31-30, 31-35, 31-40- (25-point to 40-point carbon) 
are intended primarily for structural purposes in a heat treated 
condition (Heat Treatment H or K). Steel 31-25 may be used 
for case-hardening, as also may Steel 31-30, if necessary. 

Steels 31-45, 31-50 (45-point and 50-point carbon) may be 
used for gears and other structural parts where a high degree 
of strength and hardness is demanded and where toughness is 
not of first importance. Heat Treatment K is recommended for 
such parts, the final drawing (Operation 5) being carried out at 
250° to 550° F., or at such temperature as will give the desired 
physical characteristics, 



82 



STEEL AND ITS TREATMENT 
Physical Characteristics 



Steels 31-15, 31-20 



Annealed 



Heat Treat- 
ment H or K 



Yield point or elastic limit, lbs. per sq. in. 



Reduction of area . 
Elongation in 2 in. 



30,000 

to 
40,000 

55-40% 
35-25% 



40,000 

to 
100,000 
54-40% 

25-15% 



steels 31-25, 31-30 


Annealed 


Heat Treat- 
ment H or K 


Yield point or elastic limit, lbs. per sq. in. . . . 

Reduction of area 

Elongation in 2 in 


40,000 

to 
55,000 

50-35% 
30-20% 


50,000 

to 
125,000 

55-25% 
25-10% 



Steels 31-35, 31-40 



Annealed 



Heat Treat- 
ment H or K 



Yield point or elastic limit, lbs. per sq. in. 



Reduction of area. 
Elongation in 2 in. 



45,000 

to 
60,000 

45-30% 
25-15% 



55,000 

to 
150,000 

50-25% 
20- 5% 



Steels 31-45, 31-50 



Annealed 



Heat Treat- 
ment H or K 



Yield point or elastic limit, lbs. per sq. in. 



Reduction of area. 
Elongation in 2 in 



55,000 

to 

70,000 

50-30% 

25-15% 



60,000 

to 
175,000 
45-20% 

15- 5% 



STEEL AND ITS TREATMENT 83 

Specifications Nos. 32-15 to 32-50 

Medium-Nickel Chromium Steels 

It will be noted that this type of nickel chromium steel is of 
the same composition as the preceding type, except that it con- 
tains more nickel and more chromium. 

The physical characteristics are omitted for the reason that 
results will be obtained that are intermediate between the low- 
nickel chromium alloys and the high-nickel chromium alloys. 

Specification No. 33-25 

25-Point Carbon, High-Nickel Chromium Steel 

This quality of nickel chromium steel is intermediate between 
that preferred for case-hardening (Steel 33-20) and the next 
higher quality (Steel 33-30) for heat treated structural parts. 

With the case-hardening treatment (Heat Treatment L) there 
may be slight modifications necessary. 

When properly heat treated this steel will answer for many 
structural parts. Heat Treatment M or P is recommended. 

Heat Treatment L 
After forging or machining: 

1. Carburize at a temperature between 871° C. and 955° C. 

(1600° F. and 1750° F.), (1650° F. to 1700° F. desired). 

2. Cool slowly in the carburizing mixture. 

3. Reheat to 766° C. to 816° C. (1400° F. to 1500° F.). 

4. Quench. 

5. Reheat to 705° C. to 760° C. (1300° F. to 1400° F.). 

6. Quench. 

7. Reheat to 121° C. to 260° C. (250° F. to 500° F.), and cool 

slowly. 



84 



STEEL AND ITS TREATMENT 



Heat Treatment M 
After forging or machining: 

1. Reheat to 746° C. to 774° C. (1375° F. to 1425° F.). 

2. Quench. 

3. Reheat to a temperature between 260° C. and 677° C. 

(500° F. and 1250° F.), and cool slowly. 
A higher refinement of this same treatment is: 

Heat Treatment P 
After forging or machining: 

1. Heat to 788° C. to 816° C. (1450° F. to 1500° F.). 

2. Quench. 

3. Reheat to 746° C. to 774° C. (1375° F. to 1425° F.). 

4. Quench. 

5. Reheat to a temperature between 260° C. and 677° C. 

(500° F. and 1250° F.) and cool slowly. 

Physical Characteristics 



Annealed 



Heat Treat- 
ment M or P 



Yield point or elastic limit, lbs. per sq. in. 

Reduction of area 

Elongation in 2 in 



40,000 
to 

50,000 
60-45% 
25-20% 



60,000 

to 
140,000 
65-30% 
20- 5% 



Specification No. 33-30 
30-Point Carbon, High-Nickel Chromium Steel 

This grade of nickel chromium steel is intended primarily for 
structural parts of the most important character, and should 
always be heat treated. 



STEEL AND ITS TREATMENT 



85 



This quality is suitable for crank shafts, axles, spindles, drive 
shafts, transmission shafts and, in fact, the most important 
structural parts of cars. 

The heat treatment recommended is the same as in the case 
of Steel 33-25. 

This steel is not intended for case-hardening. If case-harden- 
ing be attempted, the highest degree of care must be exercised. 



Physical Characteristics 



Annealed 



Heat Treat- 
ment L or M 



Yield point or elastic limit, lbs. per sq. in 

Reduction of area 

Elongation in 2 in 



45,000 

to 
55,000 

55-40% 
25-15% 



60,000 

to 
175,000 
60-30% 

20- 5% 



Specification No. 33-40 
40-Point Carbon, High-Nickel Chromium Steel 

This quality of steel is suitable for structural parts where 
unusual strength is demanded. Higher elastic limit is possible 
under a given treatment than with material like Steels 33-30 or 
33-35. The toughness will not be quite as great, but this does 
not bar the material from uses where toughness is not the 
controlling factor and where strength is. 

Heat Treatment P is recommended. 

This steel should be thoroughly annealed for machining. 

This quality of steel should not be case-hardened. 



STEEL AND ITS TREATMENT 
Physical Characteristics 



Yield point or elastic limit, lbs. per sq. in. 

Reduction of area 

Elongation in 2 in 



Annealed 



50,000 

to 
60,000 
50-40% 

25-15% 



Heat Treat- 
ment P 



65,000 

to 
200,000 
50-20% 

15- 2% 



Specification No. 33-45 
45-Point Carbon, High-Nickel Chromium Steel 

The use of this steel is largely for gears, where extreme strength 
and hardness are necessary. The carbon is sufficiently high to 
cause the material, in the presence of chromium and nickel, to 
become hard enough to make a good gear when quenched, with- 
out case-hardening (carburizing) . 

This steel is difficult to forge. During the forging operation 
it should be kept at a thoroughly plastic heat and not hammered 
or worked after dropping to ordinary forging temperatures, or 
cracking is liable to follow. The steel also becomes so very hard 
as to forge with great difficulty. On the other hand, too high a 
temperature is not advisable, as the steel becomes red-short and 
breaks. In brief, the forging temperature limits are narrow, and 
this steel must be reheated more frequently than any of the 
other steels dealt with in this report. 

To heat treat for gears, either Heat Treatment Q or R is 
used, the latter giving the best results. 

Heat Treatment Q 
After forging: 

1. Reheat to 802° C. to 829° C. (1475° F. to 1525° F.). (HoM 
at this temperature one-half hour to insure thorough 
heating.) 



STEEL AND ITS TREATMENT 



87 



2. Cool slowly. 

3. Reheat to 788° C. to 816° C. (1450° F. to 1500° F.). 

4. Quench. 

5. Reheat to 121° C. to 288° C. (250° F. to 550° F.) and cool 

slowly. 

This steel should be thoroughly annealed for machining 
(Operations 1 and 2). 

The final drawing operation must be conducted at a heat 
which will produce the proper degree of hardness. The desired 
Brinell hardness for a gear is between 430 and 470, the corre- 
sponding Shore hardness being from 75 to 85. 

This quality of steel should not be case-hardened. 





Physical Characteristics 






Annealed 


Heat Treat- 
ment Q 


^'ield point or elastic 
Reduction of area . . 


limit, lbs. per sq. in 


50,000 
to 

60,000 
50-40% 
25-15% 


150,000 

to 
250,000 

25-15% 
15- 2% 


Elongation in 2 in 





Heat Treatment R 
After forging: 

1. Heat to 816° C. to 844° C. (1500° F. to 1550° F.). 

2. Quench in oil. 

3. Reheat to 649° C. to 705° C. (1200° F. to 1300° F.). (Hold 

at this temperature three hours.) 

4. Cool slowly. 

5. Machine. 

6. Reheat to 732° C. to 788° C. (1350° F. to 1450° F.). 

7. Quench in oil. 

8. Reheat to 121° C. to 260° C. (250° F. to 500° F.) and cool 

slowly. 



88 STEEL AND ITS TREATMENT 

Nickel Chromium Vanadium Steels 

Specifications 41- and 42- 

The heat treatments and remarks as to application for this 
class of steels are essentially the same as for classes 31- and 32-. 
The physical characteristics obtained are very similar. 

Chromium Steels 

Specifications 51- and 52- 

The use of this type of steel is restricted almost entirely to 
ball and roller bearings. The physical characteristic most desired 
is extreme hardness. As the automobile manufacturer rarely 
works this quality of steel, no further remarks are given here. 

Chromium Vanadium Steels 
Specification No. 61-15 

15 -Point Carbon, Chromium Vanadium Steel 

Chromium vanadium steel has found much usage in automobile 
parts, particularly springs, axles, driving shafts and gears. It is 
used interchangeably with carbon steel, nickel steel and nickel 
chromium steel. 

Steel 61-15 is provided to furnish a quality that is highly 
suitable for carbonizing purposes, such as gears, and case- 
hardened parts of importance. Properly treated parts of this 
quality will be found to possess an extremely high degree of 
strength and toughness. 

This steel is also available for structural purposes, but should 
not be selected for such purposes when ordering materials. 
Better results are obtainable from some of the other qualities to 
be mentioned. 

The treatment recommended for case-hardening follows, viz.: 



STEEL AND ITS TREATMENT 



89 



Heat Treatment S 

After forging or machining: 

1. Carburize at a temperature between 871° C. and 955° C. 

(1600° F. and 1750° F.). (1650° F. to 1700° F. desired.) 

2. Cool slowly in the carburizing mixture. 

3. Reheat to 871° C. to 927° C. (1600° F. to 1700° F.). 

4. Quench. 

5. Reheat to 802° C. to 844° C. (1475° F. to 1550° F.). 

6. Quench. 

7. Reheat to 121° C. to 288° C. (250° F. to 550° F.) and cool 

slowly. 

The high initial quenching temperature of this steel is note- 
worthy; that is, something over 1600° F. This feature is different 
from other steels referred to in this report and characteristic of 
chromium vanadium steel. 

The heat to second quench (Operation 5) should be conducted 
at the lowest possible temperature that will harden the exterior 
carburized surface. Practical experiment will develop the best 
temperature for local conditions in any hardening room. 

Physical Characteristics 



Yield point or elastic limit, lbs. per sq. in. 

Reduction of area 

Elongation in 2 in 



Annealed 



35,000 
to 

45,000 
70-50% 
30-25% 



Heat Treat- 
ment T 



50,000 
to 

90,000 
70-40% 
25-10%) 



Specification 61-20 
20-Point Carbon, Chromium Vanadium Steel 
This quality is also primarily for case-hardening. It is used 
for the most important case-hardened parts; that is, case-hard- 
ened shafts, gears and the like. 



90 



STEEL AND ITS TREATMENT 



This steel may also be used in a heat treated condition for 
structural purposes, but for such work some of the specifications 
following are to be preferred, particularly where higher strength 
is desired. 

The case-hardening treatment recommended is that covered 
by Heat Treatment S. 

For structural purposes the following heat treatment is 
recommended : 

Heat Treatment T 
After forging or machining: 

1. Heat to 871° C. to 927° C. (1600° F. to 1700° F.). 

2. Quench. 

3. Reheat to some temperature between 260° C. and 705° C. 

(500° F. and 1300° F.) and cool slowly. 

Physical Characteristics 



Yield point or elastic limit, lbs. per sq. in. 



Reduction of area . 
Elongation in 2 in. 



Annealed 



40,000 
to 

50,000 
65-50% 
30-20% 



Heat Treat- 
ment T 



55,000 
to 

100,000 

65-45% 
25-10% 



Specification No. 61-25 
25-Point Carbon, Chromium Vanadium Steel 

The difference between this and the preceding specification 
is very slight and they may be used interchangeably for struc- 
tural purposes. This steel may be case-hardened, but is not 
first choice for this purpose. 

The physical characteristics may be considered as practically 
the same as given for Steel 61-20. 



STEEL AND ITS TREATMENT 
Physical Characteristics 



91 



Yield point or elastic limit, lbs. per sq. in. 

Reduction of area 

Elongation in 2 in 



Annealed 



40,000 
to 

50,000 
65-50% 
30-20% 



Heat Treat- 
ment T 



55,000 
to 

100,000 
65-45% 
25-10%o 



Specification No. 61-30 
30-Point Carbon, Chromium Vanadium Steel 

This quality of steel is intermediate in the carbon range and 
may be used interchangeably with Steel 61-25 for structural 
purposes. It should not be used for case-hardening. When 
treated as recommended by Heat Treatment T it possesses a 
high degree of combined strength and toughness. 

Physical Characteristics 





Annealed 


Heat Treat- 
ment T 


Yield point or elastic limit, lbs. per sq. in 

Reduction of area 


45,000 
to 

55,000 
60-50% 
25-20% 


60,000 
to 

150,000 

55-25% 
15- 5% 


Elongation in 2 in 





Specification No. 61-35 
35-Point Carbon, Chromium Vanadium Steel 

This Specification provides a first-rate quality of steel for 
structural parts that are to be heat treated. The fatigue- 
resisting (endurance) qualities of this material are excellent. 



92 



STEEL AND ITS TREATMENT 
Physical Characteristics 



Annealed 



Heat Treat- 
ment T 



Yield point or elastic limit, lbs. per sq. in. 

Reduction of area 

Elongation in 2 in 



45,000 
to 

55,000 
60-50% 
25-20% 



60,000 

to 
150,000 

55-25% 
15- 5% 



Specification No. 61-40 
40-Point Carbon, Chromium Vanadium Steel 

This is a very good quality of steel to be selected where a high 
degree of strength is desired, coupled with a good measure of 
toughness. Its fatigue-resisting qualities are very high, and it 
is a first-class material for high duty shafts. 

Heat Treatment T is recommended. 



Physical Characteristics 



Annealed 



Heat Treat- 
ment T 



Yield point or elastic limit, lbs. per sq. in. 

Reduction of area 

Elongation in 2 in 



50,000 

to 
60,000 

55-45% 
25-15% 



65,000 

to 
175,000 
50-15% 
15- 2% 



Specification No. 61-45 

45-Point Carbon, Chromium Vanadium Steel 

This quality of steel contains sufficient carbon in combination 
with chromium and vanadium to harden to a considerable degree 



STEEL AND ITS TREATMENT 



93 



when quenched at a proper temperature, and may be used for 
gears and springs. 

For structural parts where exceedingly high strength is de- 
sirable Heat Treatment T should be followed. 

For gears this steel should be annealed after forging and 
before machining, the anneal to consist of Operations 1 and 2 
of the following: 

Heat Treatment U 

1. Heat to 829° C. to 871° C. (1525° F. to 1600° F.). (Hold 

for about one-half hour.) 

2. Cool slowly. 

3. Reheat to 899° C. to 927° C. (1650° F. to 1700° F.). 

4. Quench. 

5. Reheat to 177° C. to 288° C. (350° F. to 550° F.) and cool 

slowly. 
This last drawing operation may be modified to obtain any 
desired hardness. 

Physical Characteristics 



Yield point or elastic limit, lbs. per sq. in . . . 



Reduction of area . 
Elongation in 2 in. 



Annealed 


Heat Treat- 
ment U 


55,000 

to 

65,000 

55-40% 

25-15% 


150,000 

to 
200,000 

25-10% 
10- 2% 



Specifications No. 61-50 
50-Point Carbon, Chromium Vanadium Steel 

Substantially the same remarks as made in regard to Steel 
61-45 apply to this quality. In this grade, however, we also 



94 



STEEL AND ITS TREATMENT 



find a material that is suitable for springs. With a proper sequence 
of heating, quenching and drawing, very high elastic limits are 
obtained. 

For spring material Heat Treatment U is recommended, except 
that the last drawing (Operation 5) will be carried farther — 
probably from 377° C. to 594° C. (700° F. to 1100° F.). This 
final drawing temperature will have to vary with the section of 
material being handled, whether light spiral springs or heavy 
flat springs. 

Physical Characteristics 



Yield point or elastic limit, lbs, per sq. in. 



Reduction ot area 



Annealed 



60,000 

to 

70,000 

50-35% 



Heat Treat- 
ment U 



150,000 

to 

225.000 

10-2% 



Helpful Hints 

It being difficult to embody in a treatise of this nature all the 
various troubles occurring in a hardening plant, the remainder 
of this text will be devoted to paragraphs on "Helpful Hints." 



Furnaces for Case-Hardening 

In building or constructing a furnace for case-hardening, the 
size of the work to be hardened should be the first consideration. 
It is far better to use a small furnace with a small box whenever 
possible. If the work varies in size, different sizes of furnaces 
may be used. Small furnaces require less fuel and small work 
must be placed in small boxes, as otherwise the pieces packed 
near the sides will be over-heated, while those in the center will 
not reach the required temperature. 



STEEL AND ITS TREATMENT 95 

Thick walls should be used to retain the heat. These walls 
should be supported by a substantial concrete foundation, so 
that they will retain their position and shape, even when sub- 
jected to a high heat. Large flues should be provided to carry 
away the smoke and gases. 

The furnace should also be so constructed that as much as 
possible of the heat of the combustion gases may be extracted 
before they are discharged. The flues and all parts of the furnace 
should be easily accessible, and a door, the full width of the oven, 
should be provided so that the tiles can be taken out and the 
flues cleaned. A pressure blower with a light oil should be used 
with all the pipes accessible and placed, preferably, above the 
furnace. If, however, they are placed below ground, they should 
be arranged in compartments which can be easily reached if 
repairs are required. 

The blower pipes should be run through the furnace so as to 
preheat the air used; if cold air is used directly it will reduce 
the heat in the furnace. The furnace fronts should be made in 
several parts to prevent cracking, with the door properly balanced 
and lined. A shelf should be provided, projecting at the front, 
for holding the boxes when they are taken out or put into the 
furnace. The smokestack should be made of sufficient height 
to produce a good draft. 

Burners should be placed both at the front and rear of the 
oven and should be arranged in separate compartments, so that 
the heat will be uniform in the oven. The hot gases will then 
pass over the top of the compartment wall and strike the boxes 
on the top, after which they pass out through small openings in 
the corner of the furnace. They then take a zigzag course under 
the tiles and pass from there through a flue to the rear of the 
furnace. A large conduit should be provided just below the 
ground which will catch all the soot. This conduit should be 
provided with iron covers which can easily be taken off to remove 
the accumulation of soot. 



96 STEEL AND ITS TREATMENT 

The furnace should not be heated too quickly, as this is apt to 
crack the brickwork. The cooling should also be done gradually. 
After the work has been taken out and the heat shut off for the 
day, all the dampers should be closed to hold the heat. In this 
way the furnace will cool slowly and cracking or bulging out of 
shape will be prevented. In addition, it will be easier to heat the 
furnace the next morning, as it will have retained some of the 
heat. 

When work is to be annealed, it should be placed in the furnace 
after the work to be hardened has been removed, and then the 
furnace brought to the proper heat. 

The material to be annealed can remain in the furnace until 
the next morning with the furnace closed and the burners turned 
off. 

The location of the pyrometer fire ends should be far from 
the live action of the flame, but should be placed either in the 
back or side of the furnace below the level of the arch or flue, 
where it would record the actual temperature of the furnace. 

Fire ends should be protected with steel or porcelain pipe. 
It is- advisable to use nickel alloy tubes, as the carbon steel 
tubes oxidize very rapidly and the porcelain tubes are very 
brittle and easily broken. 

It is also advisable to have the fire ends loose at all times, so 
when the protective case breaks the couple is safe and can be 
placed back in the furnace with a new case or pipe without 
calibration. 

A portable pyrometer should be used to check up heats fre- 
quently, as fire ends are liable to vary from time to time. 

Local Hardening 

In many cases it is essential that the piece of work be hardened 
at a certain place and that other parts be left soft. There are 



STEEL AND ITS TREATMENT 97 

three ways In which this can be accomplished: First, by copper- 
plating and enameling; second, by covering the part which is 
not to be hardened with fire clay; and third, by using a bush- 
ing or collar to cover the part to be left soft. 

In the first case the article should be painted with enamel 
where it is to be hardened, the enamel being baked after having 
been applied. The remainder of the piece that is to be left soft 
is copper-plated. In the second case, if the article to be hardened 
has a recess, such as a hole, slot, etc., this may be filled with clay. 
The third method is used when a shaft, for example, is to be 
left soft only for a short distance. A collar is then placed on the 
shaft, and this provides the easiest and least expensive means 
for accomplishing the purpose. 

In the case where enamel and copper-plating is used, the 
enamel will burn away and allow the surface covered by it to ab- 
sorb carbon and, hence, to be hardened, whereas the copper will 
stand a very high heat and prevent hardening of those portions 
that are covered by it. If the copper is burned off, it is an 
indication that the work has been overheated. The clay prevents 
the hardening of a portion of the work in the same way as does 
the copper. It is also of advantage when dipping the work, as 
it prevents the formation of steam pockets which are apt to 
warp or distort the piece. When a sleeve or collar is used this 
should be made about one inch longer than the part which is to 
be left soft, so as to prevent carburization near the ends of the 
collar. 

Heating 

The flame should be neutral or slightly rich in gas. This 
will prevent scaling for forging purposes and surface decarburiza- 
tion in annealing and heat treating. 

With a muffle furnace, of course, this precaution does not 
apply. All dies and tools of very fine edge should be heated in 
a muffle furnace or packed with charcoal in heating to the hard- 



98 STEEL AND ITS TREATMENT 

ening point. This method will give the hardest possible surface 
with the least possible oxidation. 

Great care should be exercised in the time required to bring 
the object to the right temperature. Heating should not be 
rapid, except possibly in the case of large objects, where the 
heating of the interior lags behind that of the exterior. This 
should apply only to the early part of the heating; the final 
approach to the correct temperature should be slow and uniform. 

Heating in Lead 

Heating in lead is used extensively where only a slight varia- 
tion in temperature is permissible. There are a number of un- 
satisfactory conditions, including: (1) the density of the lead and 
the necessity of holding the pieces in the lead by some mechanical 
means; (2) the purity of the lead. The lead should be as pure 
as possible and especially free from sulphur. Trouble is some- 
times experienced by the lead sticking to the work. This can be 
avoided by dipping the articles in a solution of cyanide of potas- 
sium and water — about one pound of the powdered cyanide to 
one gallon of boiling water. This should be used cold and the 
articles permitted to dry before putting them in the lead bath. 
The pieces should be left in the lead long enough to come to the 
temperature of the bath, but not permitted to remain in the 
lead longer than heating through. The pieces can be quenched 
in oil, water or brine, as preferred. 

To clean a lead pot it is advisable to add dry, common salt 
and stir thoroughly with the molten lead. All dirt and foreign 
matter will rise to the surface, which can be skimmed off with 
ease. 

Heating in Salt 

There is a good deal of difference of opinion regarding the 
method of heating in salt for hardening purposes. Barium 
chloride has been used quite extensively, and seems to work 



STEEL AND ITS TREATMENT 99 

perfectly clean at first; but after having been used for some 
time it begins to pit the steel, which is probably due to the oxide 
dissolved in the metal salts. If the barium chloride is replaced 
it then works satisfactorily again. As long as this constant 
replacement goes on good results are obtained. 

There are other salts that seem to give satisfactory results. 
One of the large steel plants uses a mixture of calcium chloride 
and sodium chloride ; about three parts of the former to one part 
of the latter. This combination melts at about 900°Fahr., and 
so is low enough to prevent the cooling effect of the steel 
from solidifying the bath. One advantage of the salt bath is 
that no bad results come from the material of the bath adhering 
to the object. When the latter is quenched the salt is solidified 
and cracks off. 

Heating in Cyanide 

Cyanide of potassium is also used as a reheating medium. 
It prevents scaling and spots. 

It has a tendency to add an additional percentage of carbon 
to the outside surface of pieces when used as a reheating medium. 

Warping 

Warping may be caused by several factors, the two most im- 
portant of which are not having the steel in a proper condition 
of repose before it is hardened and not putting the piece in the 
quenching bath properly. As any operation of working steel is 
liable to set up internal strains it is always best after rolling, 
forging or machining steel to thoroughly anneal the piece before 
hardening it. This allows the piece to assume its natural state 
of repose. In the machining operation the roughing cuts could 
be taken off, the piece annealed, then the finishing cut could be 
given it and the piece hardened. This would also make the steel 
easier to machine, as the metal is more uniform and in its softest 
state. 



100 ^ STEEL AND ITS TREATMENT 

There are several rules that can be followed in hardening a 
piece of steel to prevent warping, and these rules always assume 
that the piece has been properly annealed before starting the 
hardening operations. 

First — A piece should never be thrown into the bath, as by 
laying on the bottom it would be liable to cool faster on one 
side than the other, and thus cause warping. 

Second — The piece should be agitated in the bath to destroy 
the coating of vapor which might prevent its cooling rapidly, 
and also to allow the bath to convey its acquired heat to the 
atmosphere. 

Third — ^Work should be quenched in the direction of its prin- 
cipal axis of symmetry, so that the liquid will cover the greatest 
possible surface at the instant of quenching. A gear wheel should 
be hardened perpendicular to its plane and a shaft vertically. 

Straightening Work After Hardening 

On account of the manner in which steel is rolled, drawn or 
forged, the density varies in different parts of the steel, and no 
matter whether the material is heat treated or not, it will warp 
more or less when hardened. It is, therefore, necessary to provide 
apparatus for straightening the work. In straightening, it is 
necessary to bend the work about twice as much as would be 
required to merely keep it straight while the pressure is applied, 
as, on account of its elasticity, it will have a tendency to work 
back to its original form. Small rollers and shafts can best be 
straightened in a vise by having a 3-point contact on the jaws. 
For large diameters a special straightener will be required. A 
surface plate placed to the height of a man's eye, and at a slight 
angle towards the light, provides the easiest means for testing 
work of this character while being straightened. 

When there is a large quantity of rings to be straightened or 
trued up, a surface plate can be readily rigged up in the following 



STEEL AND ITS TREATMENT 101 

manner: A solid strap is provided on one side and a compound 
lever on the other, adjustable to any place along the plate by 
means of a slot in the latter. By a slight movement of the lever 
the ring can be trued up. An indicator should be placed at the 
front of the plate so that the operator can try a ring to see at 
which points the ring is out, and also the amount necessary for 
making it round. In straightening washers or flat pieces of any 
kind, the hydraulic press provides the best possible means. It 
might be well to mention that washers or flat pieces should be 
ground by taking a small, amount off each side alternately, as, 
otherwise, they will return to their original warped shape. 
Another precaution, relating to the grinding of cylindrical sur- 
faces, is to use a copious supply of water, as otherwise the heat 
of the grinding operation will draw the surface, producing soft 
spots. These will appear to have been caused by improper case- 
hardening, but as a matter of fact, they are wholly produced 
during the grinding operation. 

Carburizing Materials 

All carburizing material should be kept clean. The time is 
well spent in removing iron scale and fire clay from the car- 
burizing material, as these foreign materials cause soft spots. 

The carburizing material should be kept dry, as moisture 
tends to pit the work and causes soft spots. 

To lute the lid upon a carburizing pot it is advisable to use 
one-half fire clay and one-half sand, which lessens the cracking 
and breaking of the seal. 

Pipes of suitable diameters can be used for carburizing cam- 
shafts, spindles, etc., and placed in the furnace in a horizontal 
position. 

All work to be ground after carburizing should possess a 
carburized case pf a carbon content above 90 point, otherwise 
you would grind below the carbon point which gives the hardest 



102 STEEL AND ITS TREATMENT 

possible surface. This is often the cause of soft spots in car- 
burizing. 

Calibration of Pyrometers 

The calibration of a pyrometer may be accomplished readily 
and accurately without the use of an extensive laboratory equip- 
ment. The easiest and most convenient method is that based 
upon determining the melting point of common table salt (sodium 
chloride). Chemically pure salt, which is neither expensive nor 
difficult to procure, should be used where accuracy is desired. 
The salt is melted in a clean crucible of fire clay, iron or nickel, 
either in a furnace or over a forge fire, and then further heated 
until a temperature of about 875° to 900° C. (1607° to 1652° F.) 
is attained. It is essential that this crucible be clean, because a 
slight admixture of a foreign substance might noticeably lower 
or raise the melting point. 

The thermocouple to be calibrated is then removed from its 
protecting tube and its hot end is immersed in the salt bath. 
When this end has reached the temperature of the bath the 
crucible is removed from the source of heat and allowed to cool, 
and while cooling readings are taken every ten seconds on the 
voltmeter. 

A curve is then plotted by using time and temperature as 
co-ordinates, and the temperature of the melting point of salt, 
as indicated by this particular thermocouple, is noted — at the 
point, namely, where the temperature of the bath remains tem- 
porarily constant while the salt is freezing. The length of time 
during which the temperature is stationary depends on the size 
of the bath and the rate of cooling, and is not a factor in the cali- 
bration. The true melting point of salt is 801° C. (1474° F.), 
and the needed correction for the instrument under observation 
can be readily applied. 



STEEL AND ITS TREATMENT 103 

Table of Tempering Heats Showing Colors Corresponding to 
Different Temperatures 

Color 

215.6° C. 420° F Very faint yellow 

221.1° C. 430° F Very pale yellow 

226.7° C. 440° F Light yellow 

232.2° C. 450° F Pale straw yellow 

237.8° C. 460° F Deep straw yellow 

243.2° C. 470° F Dark yellow— Straw yellow 

248.9° C. 480° F Deep straw 

254.4° C. 490° F Yellow brown 

260.0° C. 500° F Brown yellow 

265.6° C. 510° F Spotted red brown 

271.7° C. 520° F Brown purple 

276.7° C. 530° F Light purple 

282.2° C. 540° F Full purple 

287.8° C. 550° F Dark purple 

293.3° C. 560° F Full blue 

298.9° C. 570° F Dark blue 

315.6° C. 600° F Very dark blue 

Hardening Heats 

Color 

400° C. 752° F Red— Visible in the dark 

474° C. 885° F Red— Visible at twilight 

525° C. 975° F Red— Visible at daylight 

581° C. 1077° F Red— Visible at sunlight 

700° C. 1292° F Dark red 

800° C. 1472° F Dull cherry red 

900° C. 1652° F Cherry red 

1000° C 1832° F Bright cherry red 

1100° C. 2012° F Orange red 

1200° C. 2192° F Orange yellow 

1300° C. 2372° F Yellow white 

1400° C. 2552° F White: Welding 

1500° C. 2732° F Brilliant white 

1600° C. 2912° F Bluish white 



To Reduce the Degrees of a Fahrenheit Thermometer 

to Those of Reaumer and the Centigrade, 

and Contrariwise 

Fahrenheit to Reaumer. — // above the freezing point. — Subtract 
32 from the number of degrees; multiply the remainder by 4, 
and divide the product by 9. 

Thus, 212°— 32° = 180°, and 180°X4^9 = 80°. 



104 STEEL AND ITS TREATMENT 

If below the freezing point. — Add 32 to the number of degrees; 
multiply the remainder by 4, and divide the product by 9. 

Thus, 40°+32° = 72°, and 72°X4-^9= -32°. 

Reaumer to Fahrenheit. — ^Multiply the number of degrees by 
9, and divide the product by 4. Then when they are above the 
freezing point, add 32 to the quotient, and when they are below, 
subtract 32. 

. Thus, 80°X9^4=180, and 180 + 32 = 212°. 
— 32°X9-^4 = 72, and 72—32 = 40°. 

Fahrenheit to Centigrade. — // above the freezing point. — Sub- 
tract 32 from the number of degrees; multiply the remainder 
by 5, and divide the product by 9. 

Thus, 212°-32°X5^9 = 180X5^9 = 100°, 

If below the freezing point. — Add 32 to the number of degrees; 
multiply the remainder by 5, and divide the product by 9. 

Thus, — 40° + 32 X5^9 = 72 X5^9 = - 40°. 

Centigrade to Fahrenheit. — Multiply the number of degrees 
by 9, and divide the product by 5. Then, when they are above 
the freezing point, add 32 to the quotient, and when they are 
below, subtract 32. 

Thus, 100°X9^5 = 180, and 180 + 32 = 212°. 
— 10°X9^5 = 18, and 18—32 = 14°. 

Reaumer to Centigrade. — -Multiply by .25 and add the product; 
or divide by 4, and add that product. 

Thus, 80°X.25 = 20, and 20 + 80 = 100°. 

Or, 80°-^4 = 20, and 20 + 80 = 100°. 

Centigrade to Reaumer. — Divide by 5 and subtract the product. 

Thus, 100°-^5 = 20, and 20—100 = 80°. 



